Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$ 5
Maximum Length of Time Hedged in Cash Flow Hedge	20 years
Credit Derivative, Maximum Exposure, Undiscounted	$ 7	$ 12
Credit Risk Derivatives, at Fair Value, Net Asset (Liability) (less than)	$ 1	$ (1)