Investment Securities (Investments Classified by Contractual Maturity Date) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	$ 154	$ 108
Available-for-sale debt securities, Due after one year through five years, Amount	2,648	2,676
Available-for-sale debt securities, Due after five years through ten years, Amount	2,887	1,383
Available-for-sale debt securities, Due after ten years, Amount	11,173	11,064
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	153	108
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	2,631	2,674
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,845	1,374
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	11,103	11,060
Available-for-sale debt securities, Yield	2.50%	2.50%
Available-for-sale debt securities, Due in one year or less, Yield	1.40%	2.70%
Available-for-sale debt securities, Due after one year through five years, Yield	1.90%	1.90%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.20%	2.40%
Available-for-sale debt securities, Due after ten years, Yield	2.70%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	16,732	15,216
Available-for-sale Securities, Debt Securities	16,862	15,231
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	83	7
Available-for-sale debt securities, Due after one year through five years, Amount	685	677
Available-for-sale debt securities, Due after five years through ten years, Amount	1,920	494
Available-for-sale debt securities, Due after ten years, Amount	0	0
Available-for-sale debt securities, Yield	1.80%	1.50%
Available-for-sale debt securities, Due in one year or less, Yield	0.20%	3.00%
Available-for-sale debt securities, Due after one year through five years, Yield	1.20%	1.20%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.00%	1.90%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	2,673	1,195
Available-for-sale Securities, Debt Securities	2,688	1,178
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	30	34
Available-for-sale debt securities, Due after one year through five years, Amount	25	12
Available-for-sale debt securities, Due after five years through ten years, Amount	104	106
Available-for-sale debt securities, Due after ten years, Amount	365	254
Available-for-sale debt securities, Yield	3.60%	3.70%
Available-for-sale debt securities, Due in one year or less, Yield	2.00%	1.90%
Available-for-sale debt securities, Due after one year through five years, Yield	3.00%	2.10%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.00%	3.00%
Available-for-sale debt securities, Due after ten years, Yield	3.90%	4.30%
Available-for-sale Debt Securities, Amortized Cost Basis	506	389
Available-for-sale Securities, Debt Securities	524	406
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	0	0
Available-for-sale debt securities, Due after one year through five years, Amount	122	128
Available-for-sale debt securities, Due after five years through ten years, Amount	93	104
Available-for-sale debt securities, Due after ten years, Amount	0	0
Available-for-sale debt securities, Yield	2.80%	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	2.60%	2.50%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.00%	2.90%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	202	224
Available-for-sale Securities, Debt Securities	215	232
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	34
Available-for-sale debt securities, Due after one year through five years, Amount	51	58
Available-for-sale debt securities, Due after five years through ten years, Amount	5	0
Available-for-sale debt securities, Due after ten years, Amount	10,249	10,333
Available-for-sale debt securities, Yield	2.70%	2.60%
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	3.10%
Available-for-sale debt securities, Due after one year through five years, Yield	2.10%	2.10%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.00%	0.00%
Available-for-sale debt securities, Due after ten years, Yield	2.70%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	10,246	10,431
Available-for-sale Securities, Debt Securities	10,305	10,425
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	0
Available-for-sale debt securities, Due after one year through five years, Amount	28	30
Available-for-sale debt securities, Due after five years through ten years, Amount	0	0
Available-for-sale debt securities, Due after ten years, Amount	284	223
Available-for-sale debt securities, Yield	1.60%	1.50%
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	1.60%	1.80%
Available-for-sale debt securities, Due after five years through ten years, Yield	0.00%	0.00%
Available-for-sale debt securities, Due after ten years, Yield	1.50%	1.40%
Available-for-sale Debt Securities, Amortized Cost Basis	313	254
Available-for-sale Securities, Debt Securities	312	253
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	1,290	1,311
Available-for-sale debt securities, Due after five years through ten years, Amount	533	463
Available-for-sale debt securities, Due after ten years, Amount	243	217
Available-for-sale debt securities, Yield	2.00%	1.90%
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	2.00%	1.90%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.00%	2.00%
Available-for-sale debt securities, Due after ten years, Yield	2.10%	2.20%
Available-for-sale Debt Securities, Amortized Cost Basis	2,061	1,989
Available-for-sale Securities, Debt Securities	2,066	1,991
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale debt securities, Due in one year or less, Amount	41	33
Available-for-sale debt securities, Due after one year through five years, Amount	447	460
Available-for-sale debt securities, Due after five years through ten years, Amount	232	216
Available-for-sale debt securities, Due after ten years, Amount	32	37
Available-for-sale debt securities, Yield	3.20%	3.20%
Available-for-sale debt securities, Due in one year or less, Yield	3.30%	3.10%
Available-for-sale debt securities, Due after one year through five years, Yield	2.70%	2.70%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.80%	3.80%
Available-for-sale debt securities, Due after ten years, Yield	5.70%	5.60%
Available-for-sale Debt Securities, Amortized Cost Basis	731	734
Available-for-sale Securities, Debt Securities	$ 752	$ 746