management 2019s discussion and analysis 78 jpmorgan chase & co./2018 form 10-k treasury and cio overview treasury and cio is predominantly responsible for measuring , monitoring , reporting and managing the firm 2019s liquidity , funding , capital , structural interest rate and foreign exchange risks . the risks managed by treasury and cio arise from the activities undertaken by the firm 2019s four major reportable business segments to serve their respective client bases , which generate both on- and off- balance sheet assets and liabilities . treasury and cio seek to achieve the firm 2019s asset-liability management objectives generally by investing in high- quality securities that are managed for the longer-term as part of the firm 2019s investment securities portfolio . treasury and cio also use derivatives to meet the firm 2019s asset- liability management objectives . for further information on derivatives , refer to note 5 . in addition , treasury and cio manage the firm 2019s cash position primarily through depositing at central banks and investing in short-term instruments . for further information on liquidity and funding risk , refer to liquidity risk management on pages 95 2013100 . for information on interest rate , foreign exchange and other risks , refer to market risk management on pages 124 2013131 . the investment securities portfolio primarily consists of agency and nonagency mortgage-backed securities , u.s . and non-u.s . government securities , obligations of u.s . states and municipalities , other abs and corporate debt securities . at december 31 , 2018 , the investment securities portfolio was $ 260.1 billion , and the average credit rating of the securities comprising the portfolio was aa+ ( based upon external ratings where available and , where not available , based primarily upon internal ratings that correspond to ratings as defined by s&p and moody 2019s ) . refer to note 10 for further information on the firm 2019s investment securities portfolio . selected income statement and balance sheet data as of or for the year ended december 31 , ( in millions ) 2018 2017 2016 investment securities gains/ ( losses ) $ ( 395 ) $ ( 78 ) $ 132 available-for-sale ( 201cafs 201d ) investment securities ( average ) 203449 219345 226892 held-to-maturity ( 201chtm 201d ) investment securities ( average ) 31747 47927 51358 investment securities portfolio ( average ) 235197 267272 278250 afs investment securities ( period-end ) 228681 200247 236670 htm investment securities ( period-end ) 31434 47733 50168 investment securities portfolio ( period 2013end ) 260115 247980 286838 as permitted by the new hedge accounting guidance , the firm elected to transfer certain investment securities from htm to afs in the first quarter of 2018 . for additional information , refer to notes 1 and 10. .

2018: investment securities gains/ ( losses ): -395
available-for-sale ( 201cafs 201d ) investment securities ( average ): 203449
held-to-maturity ( 201chtm 201d ) investment securities ( average ): 31747
investment securities portfolio ( average ): 235197
afs investment securities ( period-end ): 228681
htm investment securities ( period-end ): 31434
investment securities portfolio ( period 2013end ): 260115
2017: investment securities gains/ ( losses ): -78
available-for-sale ( 201cafs 201d ) investment securities ( average ): 219345
held-to-maturity ( 201chtm 201d ) investment securities ( average ): 47927
investment securities portfolio ( average ): 267272
afs investment securities ( period-end ): 200247
htm investment securities ( period-end ): 47733
investment securities portfolio ( period 2013end ): 247980
2016: investment securities gains/ ( losses ): 132
available-for-sale ( 201cafs 201d ) investment securities ( average ): 226892
held-to-maturity ( 201chtm 201d ) investment securities ( average ): 51358
investment securities portfolio ( average ): 278250
afs investment securities ( period-end ): 236670
htm investment securities ( period-end ): 50168
investment securities portfolio ( period 2013end ): 286838

management 2019s discussion and analysis 78 jpmorgan chase & co./2018 form 10-k treasury and cio overview treasury and cio is predominantly responsible for measuring , monitoring , reporting and managing the firm 2019s liquidity , funding , capital , structural interest rate and foreign exchange risks . the risks managed by treasury and cio arise from the activities undertaken by the firm 2019s four major reportable business segments to serve their respective client bases , which generate both on- and off- balance sheet assets and liabilities . treasury and cio seek to achieve the firm 2019s asset-liability management objectives generally by investing in high- quality securities that are managed for the longer-term as part of the firm 2019s investment securities portfolio . treasury and cio also use derivatives to meet the firm 2019s asset- liability management objectives . for further information on derivatives , refer to note 5 . in addition , treasury and cio manage the firm 2019s cash position primarily through depositing at central banks and investing in short-term instruments . for further information on liquidity and funding risk , refer to liquidity risk management on pages 95 2013100 . for information on interest rate , foreign exchange and other risks , refer to market risk management on pages 124 2013131 . the investment securities portfolio primarily consists of agency and nonagency mortgage-backed securities , u.s . and non-u.s . government securities , obligations of u.s . states and municipalities , other abs and corporate debt securities . at december 31 , 2018 , the investment securities portfolio was $ 260.1 billion , and the average credit rating of the securities comprising the portfolio was aa+ ( based upon external ratings where available and , where not available , based primarily upon internal ratings that correspond to ratings as defined by s&p and moody 2019s ) . refer to note 10 for further information on the firm 2019s investment securities portfolio . selected income statement and balance sheet data as of or for the year ended december 31 , ( in millions ) 2018 2017 2016 investment securities gains/ ( losses ) $ ( 395 ) $ ( 78 ) $ 132 available-for-sale ( 201cafs 201d ) investment securities ( average ) 203449 219345 226892 held-to-maturity ( 201chtm 201d ) investment securities ( average ) 31747 47927 51358 investment securities portfolio ( average ) 235197 267272 278250 afs investment securities ( period-end ) 228681 200247 236670 htm investment securities ( period-end ) 31434 47733 50168 investment securities portfolio ( period 2013end ) 260115 247980 286838 as permitted by the new hedge accounting guidance , the firm elected to transfer certain investment securities from htm to afs in the first quarter of 2018 . for additional information , refer to notes 1 and 10. .

Questions:
what was the amount of the afs investment securities in 2018?
and what was it in 2017?
what was, then, the combined total for the two years?
including 2016, what then becomes this total?
and what was the average between the three years?
and between the last two years of that period, from 2017 to 2018, what was the change in the ending available for sale investment securities?

Answers:
228681
200247
428928
665598
221866
28434