Debt (Debt Textuals) (Details) - USD ($) $ in Millions |
3 Months Ended | 12 Months Ended | ||
|---|---|---|---|---|
Mar. 31, 2016 |
Dec. 31, 2015 |
Feb. 08, 2016 |
Mar. 31, 2015 |
|
| Debt Instruments [Abstract] | ||||
| Prior Period Reclassification Adjustment | $ 152 | |||
| Debt Instrument, Interest Rate, Effective Percentage | 5.50% | 5.70% | ||
| Corporate Revolving Credit Facility [Member] | ||||
| Line of Credit Facility [Line Items] | ||||
| Line of Credit Facility, Increase (Decrease), Net | $ 178 | |||
| Line of Credit Facility, Maximum Borrowing Capacity | $ 1,678 | |||
| Future line of credit facility maximum borrowing capacity on June 27, 2018 | $ 1,520 | |||
| Increase in Letter of Credit Sublimit | 250 | |||
| Total Letter of Credit Sublimit | $ 1,000 | |||
| Extension of Line of Credit Revolver | 2 years |