Investment Securities (Investments, by type and length in continuous loss position) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	$ 266	$ 1,435
Gross unrealized losses, less than 12 months	11	241
Estimated fair value, 12 months or more	942	836
Gross unrealized losses, 12 months or more	316	169
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	81	87
Gross unrealized losses, less than 12 months	1	1
Estimated fair value, 12 months or more	316	307
Gross unrealized losses, 12 months or more	119	142
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	18	219
Gross unrealized losses, less than 12 months	0	9
Estimated fair value, 12 months or more	709	825
Gross unrealized losses, 12 months or more	141	277
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	56	244
Gross unrealized losses, less than 12 months	1	23
Estimated fair value, 12 months or more	1,006	1,320
Gross unrealized losses, 12 months or more	125	224
Asset-backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	9	100
Gross unrealized losses, less than 12 months	2	7
Estimated fair value, 12 months or more	746	850
Gross unrealized losses, 12 months or more	109	157
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	138	330
Gross unrealized losses, less than 12 months	10	28
Estimated fair value, 12 months or more	622	607
Gross unrealized losses, 12 months or more	124	179
Foreign Government Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	142	906
Gross unrealized losses, less than 12 months	1	5
Estimated fair value, 12 months or more	94	203
Gross unrealized losses, 12 months or more	3	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	57	440
Gross unrealized losses, less than 12 months	16	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	769	4,263
Gross unrealized losses, less than 12 months	42	352
Estimated fair value, 12 months or more	4,442	4,948
Gross unrealized losses, 12 months or more	$ 938	$ 1,229