Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Components of other comprehensive income or loss [Abstract]
Unrealized holding gains arising during the year, Before tax	$ 1,029	$ 230	$ 1,930
Unrealized holding gains arising during the year, Income tax	359	81	675
Unrealized holding gains arising during the year, Net of tax	670	149	1,255
Unrealized other-than-temporary impairment losses arising during the year, Before tax	(1)	(3)	(14)
Unrealized other-than-temporary impairment losses arising during the year, Income tax	0	(1)	(5)
Unrealized other-than-temporary impairment losses arising during the year, Net of tax	(1)	(2)	(9)
Reclassification adjustment for realized gains included in net income, Before tax	81	110	44
Reclassification adjustment for realized gains included in net income, Income tax	28	39	15
Reclassification adjustment for realized gains included in net income, Net of tax	53	71	29
Net unrealized gains recognized in other comprehensive income or loss, Before tax	947	117	1,872
Net unrealized gains recognized in other comprehensive income or loss, Income tax	331	41	655
Net unrealized gains recognized in other comprehensive income or loss, Net of tax	616	76	1,217
Foreign currency translation gains (losses), Before tax	6	(28)	262
Foreign currency translation gains (losses), Income tax	2	(10)	92
Foreign currency translation gains (losses), Net of tax	4	(18)	170
Change in postretirement benefit costs not yet recognized in net income, Before tax	(329)	20	134
Change in postretirement benefit costs not yet recognized in net income, Income tax	(114)	8	36
Change in postretirement benefit costs not yet recognized in net income, Net of tax	(215)	12	98
Total other comprehensive income, Before tax	624	109	2,268
Total other comprehensive income, Income tax	219	39	783
Total Other Comprehensive Income, Net of Tax	$ 405	$ 70	$ 1,485