Investments (Fair Values And Gross Unrealized Losses By Credit Rating Category Of Corporate Obligations) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Investment [Line Items]
Total, Fair Value	$ 2,387	$ 6,954
Total, Unrealized Losses	(478)	(804)
Corporate Obligations [Member]
Investment [Line Items]
Total, Fair Value	717
Total, Unrealized Losses	(106)
Corporate Obligations [Member] | Aaa [Member]
Investment [Line Items]
Total, Fair Value	70
Corporate Obligations [Member] | Aa [Member]
Investment [Line Items]
Total, Fair Value	71
Total, Unrealized Losses	(8)
Corporate Obligations [Member] | A [Member]
Investment [Line Items]
Total, Fair Value	209
Total, Unrealized Losses	(37)
Corporate Obligations [Member] | Baa [Member]
Investment [Line Items]
Total, Fair Value	224
Total, Unrealized Losses	(35)
Corporate Obligations [Member] | Below Investment Grade [Member]
Investment [Line Items]
Total, Fair Value	27
Corporate Obligations [Member] | Not Rated [Member]
Investment [Line Items]
Total, Fair Value	116
Total, Unrealized Losses	$ (26)