Financial Instruments (Interest Rate Exposure) (Details) - USD ($) |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Derivative [Line Items] | |||
| Fair value changes reclassified from other comprehensive earnings | $ 0 | $ 9,000,000 | $ 4,000,000 |
| Interest rate swap [Member] | |||
| Derivative [Line Items] | |||
| Notional amount | 0 | ||
| Notional amount of derivatives terminated | 500,000,000 | 1,250,000,000 | |
| Fair value changes reclassified from other comprehensive earnings | 1,000,000 | 2,000,000 | |
| Gain (loss) on interest rate derivative | 0 | (7,000,000) | (17,000,000) |
| Gain (loss) reclassified from accumulated other comprehensive earnings into income | (1,000,000) | $ (9,000,000) | $ (4,000,000) |
| Forward contracts [Member] | |||
| Derivative [Line Items] | |||
| Notional amount | $ 0 | ||