Derivative Instruments (Details 4) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Jun. 30, 2015 |
Jun. 30, 2014 |
Jun. 30, 2015 |
Jun. 30, 2014 |
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| Derivative Instruments, Gain (Loss) [Line Items] | |||||||||||||
| Interest expense | $ 158 | $ 169 | $ 312 | $ 335 | |||||||||
| Interest Rate Swap [Member] | |||||||||||||
| Derivative Instruments, Gain (Loss) [Line Items] | |||||||||||||
| Gains (Loss) Recognized in OCI (Effective Portion) | [1],[2] | 14 | (9) | 8 | (9) | ||||||||
| Interest expense | 0 | 1 | 1 | 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] | $ (12) | $ (13) | $ (24) | $ (26) | ||||||||
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