Derivative Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments [Abstract]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ (50)
Derivative, Collateral, Obligation to Return Cash	27	$ 60
Margin Cash Collateral Not Netted Against Derivative Liabilities	$ 116	$ 122