Revenues increased 3% in 2017 compared to 2016. AltaLink’s operating revenues increased $197 million (39%) in 2017 compared to 2016, primarily due to effects of a decision in 2016 by its regulator, which changed the timing of when construction-in-progress expenditures included in the rate base are billable to customers and earned in revenues. The decision resulted in a one-time net reduction in revenue in 2016, with offsetting reductions in expenses. In 2017, we also experienced a comparative revenue increase of 13% from renewable energy and a comparative decline of 12% from the unregulated retail services business. Pre-tax earnings in 2017 were relatively unchanged from 2016, as increased earnings from renewable energy and AltaLink were offset by lower earnings from the unregulated retail services business and other energy ventures.
Pre-tax earnings increased $92 million (12.6%) in 2016 compared to 2015. The earnings increase reflected increased earnings from Forest River and apparel and footwear businesses, partly offset by pre-tax losses of Duracell. In 2016, Duracell incurred a pre-tax loss of approximately $89 million primarily due to significant transition, business integration and restructuring costs. Forest River generated a pre-tax earnings increase of 28%, primarily due to increased sales volumes and higher gross margins. Earnings of our apparel businesses increased 22% in 2016, primarily attributable to lower restructuring costs and a loss in 2015 from the disposition of a Fruit of the Loom operation, partly offset by lower earnings from our footwear businesses.
Pre-tax earnings were $1.3 billion in 2017, an increase of $137 million (12%) compared to 2016. The comparative increase in earnings was primarily attributable to increased earnings of NetJets and TTI, partly offset by lower earnings from FlightSafety, as well as our media and logistics businesses.
Revenues were $48.1 billion in 2016, a decline of $148 million (0.3%) compared to 2015. In 2016, we experienced a decline in grocery revenues, partly offset by an increase in foodservice revenues. Earnings were $431 million in 2016, a decrease of $71 million (14%) compared to 2015. The reduced earnings was primarily due to a reduction in McLane’s operating margin rate. The decline was primarily due to increased employee related costs. Additionally, earnings in 2015 included a gain of $19 million from the disposition of a subsidiary.
The following table summarizes the estimated effects of hypothetical changes in interest rates on our significant assets and liabilities that are subject to significant interest rate risk at December 31, 2017 and 2016. We assumed that the interest rate changes occur immediately and uniformly to each category of instrument containing interest rate risk, and that there were no significant changes to other factors used to determine the value of the instrument. The hypothetical changes in interest rates do not reflect the best or worst case scenarios. Actual results may differ from those reflected in the table. Dollars are in millions.
We classify investments in fixed maturity and equity securities at the acquisition date and re-evaluate the classification at each balance sheet date. Investments classified as held-to-maturity are carried at amortized cost, reflecting the ability and intent to hold the securities to maturity. Trading investments are securities acquired with the intent to sell in the near term and are carried at fair value with changes in fair value reported in earnings. All other securities are classified as available-for-sale and are carried at fair value with net unrealized gains or losses reported as a component of accumulated other comprehensive income. As of December 31, 2017, substantially all of our investments in equity and fixed maturity securities were classified as available-for-sale.
The equity index put option contracts are European style options written prior to March 2008 on four major equity indexes. The contracts expire between June 2018 and January 2026. Future payments, if any, under any given contract will be required if the prevailing index value is below the contract strike price at the expiration date. We received aggregate premiums of $4.2 billion on these contracts at the contract inception dates and we have no counterparty credit risk. The aggregate intrinsic value (the undiscounted liability assuming the contracts are settled based on the index values and foreign currency exchange rates as of the balance sheet date) was $789 million at December 31, 2017 and $1.0 billion at December 31, 2016. These contracts may not be unilaterally terminated or fully settled before the expiration dates and the ultimate amount of cash basis gains or losses on these contracts will not be determined until the contract expiration dates. The remaining weighted average life of all contracts was approximately 2.9 years at December 31, 2017.
A limited number of our equity index put option contracts contain collateral posting requirements with respect to changes in the fair value or intrinsic value of the contracts and/or a downgrade of Berkshire’s credit ratings. As of December 31, 2017, we did not have any collateral posting requirements. If Berkshire’s credit ratings (currently AA from Standard & Poor’s and Aa2 from Moody’s) are downgraded below either A- by Standard & Poor’s or A3 by Moody’s, collateral of up to $1.1 billion could be required to be posted.
As of December 31, 2017, our subsidiaries had unused lines of credit and commercial paper capacity aggregating approximately $7.7 billion to support short-term borrowing programs and provide additional liquidity. Such unused lines of credit included about $4.0 billion related to BHE and its subsidiaries. In addition to BHFC’s borrowings, at December 31, 2017, Berkshire guaranteed approximately $1.9 billion of other subsidiary borrowings. Generally, Berkshire’s guarantee of a subsidiary’s debt obligation is an absolute, unconditional and irrevocable guarantee for the full and prompt payment when due of all payment obligations.
Income tax expense is reconciled to hypothetical amounts computed at the U.S. federal statutory rate for each of the three years ending December 31, 2017 in the table below (in millions).
A summary of the net changes in after-tax accumulated other comprehensive income attributable to Berkshire Hathaway shareholders and significant amounts reclassified from accumulated other comprehensive income into net earnings for each of the three years ending December 31, 2017 follows (in millions).