Derivative Instruments (Details 4) (Details) - USD ($) $ in Millions |
12 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
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| Derivative Instruments, Gain (Loss) [Line Items] | ||||||||||||
| Interest expense | $ 628 | $ 645 | $ 696 | |||||||||
| Interest Rate Swap [Member] | ||||||||||||
| Derivative Instruments, Gain (Loss) [Line Items] | ||||||||||||
| Gains (Loss) Recognized in OCI (Effective Portion) | [1],[2] | 23 | (2) | 86 | ||||||||
| Interest expense | 3 | 11 | 2 | |||||||||
| Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest Rate Swap [Member] | ||||||||||||
| Derivative Instruments, Gain (Loss) [Line Items] | ||||||||||||
| Interest expense | [1],[2],[3],[4] | $ (47) | $ (46) | $ (51) | ||||||||
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