Investment Securities (Investments Classified by Contractual Maturity Date) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	$ 15,752	$ 14,178
Available-for-sale Securities, Amortized Cost Basis	15,565	13,997
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	14,767	13,026
Available-for-sale debt securities, Due in one year or less, Amount	598	432
Available-for-sale debt securities, Due after one year through five years, Amount	2,899	2,921
Available-for-sale debt securities, Due after five years through ten years, Amount	2,396	2,417
Available-for-sale debt securities, Due after ten years, Amount	8,874	7,256
Available-for-sale Securities, Amortized Cost Basis	14,579	12,804
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	598	431
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	2,852	2,880
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,352	2,369
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	8,777	7,124
Available-for-sale debt securities, Yield	2.40%	2.40%
Available-for-sale debt securities, Due in one year or less, Yield	0.10%	0.10%
Available-for-sale debt securities, Due after one year through five years, Yield	2.20%	2.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.60%	2.60%
Available-for-sale debt securities, Due after ten years, Yield	2.50%	2.60%
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	2,099	2,214
Available-for-sale debt securities, Due in one year or less, Amount	584	422
Available-for-sale debt securities, Due after one year through five years, Amount	538	682
Available-for-sale debt securities, Due after five years through ten years, Amount	977	1,110
Available-for-sale debt securities, Due after ten years, Amount	0	0
Available-for-sale Securities, Amortized Cost Basis	2,097	2,212
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	1.00%	0.70%
Available-for-sale debt securities, Due after five years through ten years, Yield	1.40%	1.40%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	306	303
Available-for-sale debt securities, Due in one year or less, Amount	3	1
Available-for-sale debt securities, Due after one year through five years, Amount	139	136
Available-for-sale debt securities, Due after five years through ten years, Amount	164	166
Available-for-sale debt securities, Due after ten years, Amount	0	0
Available-for-sale Securities, Amortized Cost Basis	297	295
Available-for-sale debt securities, Yield	3.20%	2.50%
Available-for-sale debt securities, Due in one year or less, Yield	4.30%	2.20%
Available-for-sale debt securities, Due after one year through five years, Yield	3.00%	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	0.00%	0.00%
Residential Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	8,815	6,906
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	140	35
Available-for-sale debt securities, Due after ten years, Amount	8,675	6,871
Available-for-sale Securities, Amortized Cost Basis	8,722	6,779
Available-for-sale debt securities, Yield	2.40%	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	2.30%	4.30%
Available-for-sale debt securities, Due after ten years, Yield	2.40%	2.70%
Asset-backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	2,221	2,340
Available-for-sale debt securities, Due in one year or less, Amount	7	0
Available-for-sale debt securities, Due after one year through five years, Amount	1,595	1,543
Available-for-sale debt securities, Due after five years through ten years, Amount	511	510
Available-for-sale debt securities, Due after ten years, Amount	108	287
Available-for-sale Securities, Amortized Cost Basis	2,191	2,309
Available-for-sale debt securities, Yield	2.00%	2.10%
Available-for-sale debt securities, Due in one year or less, Yield	2.00%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	2.00%	2.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	1.80%	1.70%
Available-for-sale debt securities, Due after ten years, Yield	2.60%	3.30%
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities	1,326	1,263
Available-for-sale debt securities, Due in one year or less, Amount	4	9
Available-for-sale debt securities, Due after one year through five years, Amount	627	560
Available-for-sale debt securities, Due after five years through ten years, Amount	604	596
Available-for-sale debt securities, Due after ten years, Amount	91	98
Available-for-sale Securities, Amortized Cost Basis	$ 1,272	$ 1,209
Available-for-sale debt securities, Yield	5.10%	5.10%
Available-for-sale debt securities, Due in one year or less, Yield	5.80%	3.20%
Available-for-sale debt securities, Due after one year through five years, Yield	4.10%	4.00%
Available-for-sale debt securities, Due after five years through ten years, Yield	6.00%	6.00%
Available-for-sale debt securities, Due after ten years, Yield	6.00%	5.80%