Derivative Instruments (Gains (Losses) On Derivative Instruments Designated As Cash Flow Hedges) (Details) - Designated as Hedging Instrument [Member] - Cash flow hedges - Other Comprehensive Income (Loss) [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gains (losses) on derivative instruments designated and qualifying as cash flow hedges
Offset to net investment income	$ 16	$ 14	$ (22)
Offset to realized gain (loss)	8
Offset to interest and debt expense	$ (10)	$ 1	$ 4