Investment Securities (Investments, by type and length in continuous loss position) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	$ 365	$ 1,435
Gross unrealized losses, less than 12 months	(16)	(241)
Estimated fair value, 12 months or more	1,121	836
Gross unrealized losses, 12 months or more	(311)	(169)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	71	87
Gross unrealized losses, less than 12 months	(1)	(1)
Estimated fair value, 12 months or more	233	307
Gross unrealized losses, 12 months or more	(129)	(142)
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	26	219
Gross unrealized losses, less than 12 months	0	(9)
Estimated fair value, 12 months or more	752	825
Gross unrealized losses, 12 months or more	(198)	(277)
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	268	244
Gross unrealized losses, less than 12 months	(7)	(23)
Estimated fair value, 12 months or more	1,057	1,320
Gross unrealized losses, 12 months or more	(173)	(224)
Asset-backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	4,136	100
Gross unrealized losses, less than 12 months	(27)	(7)
Estimated fair value, 12 months or more	792	850
Gross unrealized losses, 12 months or more	(121)	(157)
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	488	330
Gross unrealized losses, less than 12 months	(31)	(28)
Estimated fair value, 12 months or more	571	607
Gross unrealized losses, 12 months or more	(137)	(179)
Foreign Government Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	196	906
Gross unrealized losses, less than 12 months	(1)	(5)
Estimated fair value, 12 months or more	171	203
Gross unrealized losses, 12 months or more	(29)	(81)
US Treasury and Government [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	0	502
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, 12 months or more	0	0
Retained Interest [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	2	0
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, 12 months or more	0	0
Equity Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	64	440
Gross unrealized losses, less than 12 months	(5)	(38)
Estimated fair value, 12 months or more	7	0
Gross unrealized losses, 12 months or more	(1)	0
Total [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	5,616	4,263
Gross unrealized losses, less than 12 months	(88)	(352)
Estimated fair value, 12 months or more	4,704	4,948
Gross unrealized losses, 12 months or more	$ (1,099)	$ (1,229)