| **Leases (Maturities of Operating Lease Liabilities) (Details) $ in Millions** | Mar. 31, 2019 USD ($) |
|--------------------------------------------------------------------------------|-----------------------|
| **Leases [Abstract]**                                                          |                  |
| 2019 (Excluding the three months ended March 31, 2019)                         | $ 24                  |
| 2020                                                                           | 40                    |
| 2021                                                                           | 42                    |
| 2022                                                                           | 39                    |
| 2023                                                                           | 33                    |
| Thereafter                                                                     | 202                   |
| Total lease payments                                                           | 380                   |
| Less: Discount                                                                 | (72)                  |
| Total operating lease liabilities                                              | $ 308                 |

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| - Definition
Amount of lessee's undiscounted obligation for lease payments for operating lease.
+ References
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| - Definition
Amount of lessee's undiscounted obligation for lease payments for operating lease, due after fifth fiscal year following latest fiscal year.
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| - Definition
Amount of lessee's undiscounted obligation for lease payments for operating lease, due in fifth fiscal year following latest fiscal year.
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| - Definition
Amount of lessee's undiscounted obligation for lease payments for operating lease, due in fourth fiscal year following latest fiscal year.
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Amount of lessee's undiscounted obligation for lease payments for operating lease, due in third fiscal year following latest fiscal year.
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Amount of lessee's undiscounted obligation for lease payments for operating lease, due in second fiscal year following latest fiscal year.
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| - Definition
Amount of lessee's undiscounted obligation for lease payments for operating lease having an initial or remaining lease term in excess of one year due in remainder of fiscal year following latest fiscal year.
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| - Definition
Amount of lessee's undiscounted obligation for lease payments in excess of discounted obligation for lease payments for operating lease.
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| - Definition
Present value of lessee's discounted obligation for lease payments from operating lease.
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