Derivative Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ (80)
Derivative, Collateral, Obligation to Return Cash	5	$ 27
Margin Cash Collateral Not Netted Against Derivative Liabilities	129	$ 116
Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Derivative [Line Items]
Reclassification from AOCI, Current Period, before Tax, Attributable to Parent	18
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	$ 11