Derivatives - Fair Value Hedges (Details) - Fair value hedges - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2018 |
Jun. 30, 2017 |
Jun. 30, 2018 |
Jun. 30, 2017 |
|
| Derivatives in Fair Value Hedging Relationships | ||||
| Gain (Loss) on Derivative Recognized in income | $ (1) | $ 1 | $ (12) | $ (4) |
| Gain (Loss) on Hedged Item Recognized in Income | 1 | (1) | 12 | 4 |
| Interest rate swap contracts | Interest expense. | ||||
| Derivatives in Fair Value Hedging Relationships | ||||
| Gain (Loss) on Derivative Recognized in income | (1) | 1 | (12) | (4) |
| Gain (Loss) on Hedged Item Recognized in Income | $ 1 | $ (1) | $ 12 | $ 4 |