Investment Securities (Investments Classified by Contractual Maturity Date) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	$ 609	$ 432
Available-for-sale debt securities, Due after one year through five years, Amount	2,707	2,921
Available-for-sale debt securities, Due after five years through ten years, Amount	2,284	2,417
Available-for-sale debt securities, Due after ten years, Amount	11,450	7,256
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	609	431
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	2,694	2,880
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,323	2,369
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	11,688	7,124
Available-for-sale debt securities, Yield	2.50%	2.40%
Available-for-sale debt securities, Due in one year or less, Yield	0.20%	0.10%
Available-for-sale debt securities, Due after one year through five years, Yield	2.10%	2.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.40%	2.60%
Available-for-sale debt securities, Due after ten years, Yield	2.70%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	17,314	12,804
Available-for-sale Securities, Debt Securities	17,050	13,026
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	588	422
Available-for-sale debt securities, Due after one year through five years, Amount	505	682
Available-for-sale debt securities, Due after five years through ten years, Amount	929	1,110
Available-for-sale debt securities, Due after ten years, Amount	0	0
Available-for-sale debt securities, Yield	0.90%	0.90%
Available-for-sale debt securities, Due in one year or less, Yield	0.10%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	1.20%	0.70%
Available-for-sale debt securities, Due after five years through ten years, Yield	1.30%	1.40%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	2,075	2,212
Available-for-sale Securities, Debt Securities	2,022	2,214
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	0
Available-for-sale debt securities, Due after one year through five years, Amount	0
Available-for-sale debt securities, Due after five years through ten years, Amount	86
Available-for-sale debt securities, Due after ten years, Amount	93
Available-for-sale debt securities, Yield	3.40%
Available-for-sale debt securities, Due in one year or less, Yield	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.60%
Available-for-sale debt securities, Due after ten years, Yield	4.20%
Available-for-sale Debt Securities, Amortized Cost Basis	178	0
Available-for-sale Securities, Debt Securities	179	0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	5	1
Available-for-sale debt securities, Due after one year through five years, Amount	111	136
Available-for-sale debt securities, Due after five years through ten years, Amount	179	166
Available-for-sale debt securities, Due after ten years, Amount	5	0
Available-for-sale debt securities, Yield	3.50%	2.50%
Available-for-sale debt securities, Due in one year or less, Yield	6.10%	2.20%
Available-for-sale debt securities, Due after one year through five years, Yield	3.80%	1.80%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.00%
Available-for-sale debt securities, Due after ten years, Yield	4.10%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	299	295
Available-for-sale Securities, Debt Securities	300	303
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	0	0
Available-for-sale debt securities, Due after one year through five years, Amount	0	0
Available-for-sale debt securities, Due after five years through ten years, Amount	101	35
Available-for-sale debt securities, Due after ten years, Amount	11,105	6,871
Available-for-sale debt securities, Yield	2.70%	2.70%
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.10%	4.30%
Available-for-sale debt securities, Due after ten years, Yield	2.70%	2.70%
Available-for-sale Debt Securities, Amortized Cost Basis	11,444	6,779
Available-for-sale Securities, Debt Securities	11,206	6,906
Commercial Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	0
Available-for-sale debt securities, Due after one year through five years, Amount	0
Available-for-sale debt securities, Due after five years through ten years, Amount	0
Available-for-sale debt securities, Due after ten years, Amount	20
Available-for-sale debt securities, Yield	1.30%
Available-for-sale debt securities, Due in one year or less, Yield	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	0.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	0.00%
Available-for-sale debt securities, Due after ten years, Yield	1.30%
Available-for-sale Debt Securities, Amortized Cost Basis	20	0
Available-for-sale Securities, Debt Securities	20	0
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	0	0
Available-for-sale debt securities, Due after one year through five years, Amount	1,580	1,543
Available-for-sale debt securities, Due after five years through ten years, Amount	540	510
Available-for-sale debt securities, Due after ten years, Amount	145	287
Available-for-sale debt securities, Yield	1.90%	2.10%
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	1.90%	2.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	1.90%	1.70%
Available-for-sale debt securities, Due after ten years, Yield	2.50%	3.30%
Available-for-sale Debt Securities, Amortized Cost Basis	2,251	2,309
Available-for-sale Securities, Debt Securities	2,265	2,340
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	16	9
Available-for-sale debt securities, Due after one year through five years, Amount	511	560
Available-for-sale debt securities, Due after five years through ten years, Amount	449	596
Available-for-sale debt securities, Due after ten years, Amount	82	98
Available-for-sale debt securities, Yield	4.30%	5.10%
Available-for-sale debt securities, Due in one year or less, Yield	5.10%	3.20%
Available-for-sale debt securities, Due after one year through five years, Yield	3.30%	4.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	5.10%	6.00%
Available-for-sale debt securities, Due after ten years, Yield	5.70%	5.80%
Available-for-sale Debt Securities, Amortized Cost Basis	1,047	1,209
Available-for-sale Securities, Debt Securities	$ 1,058	$ 1,263