Adoption of New Accounting Pronouncements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Retained Earnings [Member]
Cumulative effect from adoption of new guidance [Abstract]
Cumulative effect from adoption of new guidance on recognition of other-than-temporary impairments	$ 0	$ 0	$ 30
Unrealized Appreciation (Depreciation) of Investments Including Unrealized Other-Than-Temporary Impairment Losses [Member]
Cumulative effect from adoption of new guidance [Abstract]
Cumulative effect from adoption of new guidance on recognition of other-than-temporary impairments	$ 0	$ 0	$ (30)