Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Jun. 30, 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	2,919	2,676
Available-for-sale debt securities, Due after five years through ten years, Amount	2,376	1,383
Available-for-sale debt securities, Due after ten years, Amount	12,705	11,064
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	154	108
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	2,913	2,674
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,393	1,374
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	$ 12,765	$ 11,060
Available-for-sale debt securities, Yield	2.60%	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	1.80%	1.90%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.40%	2.40%
Available-for-sale debt securities, Due after ten years, Yield	2.80%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 18,225	$ 15,216
Available-for-sale Securities, Debt Securities	18,154	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	87	7
Available-for-sale debt securities, Due after one year through five years, Amount	898	677
Available-for-sale debt securities, Due after five years through ten years, Amount	1,190	494
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Yield	1.60%	1.50%
Available-for-sale debt securities, Due in one year or less, Yield	0.50%	3.00%
Available-for-sale debt securities, Due after one year through five years, Yield	1.10%	1.20%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.10%	1.90%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,203	$ 1,195
Available-for-sale Securities, Debt Securities	2,175	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	24	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	110	106
Available-for-sale debt securities, Due after ten years, Amount	$ 410	$ 254
Available-for-sale debt securities, Yield	3.50%	3.70%
Available-for-sale debt securities, Due in one year or less, Yield	2.70%	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	2.80%	3.00%
Available-for-sale debt securities, Due after ten years, Yield	3.80%	4.30%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 562	$ 389
Available-for-sale Securities, Debt Securities	569	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	6	0
Available-for-sale debt securities, Due after one year through five years, Amount	100	128
Available-for-sale debt securities, Due after five years through ten years, Amount	94	104
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Yield	2.60%	2.70%
Available-for-sale debt securities, Due in one year or less, Yield	1.20%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	2.50%	2.50%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.70%	2.90%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 191	$ 224
Available-for-sale Securities, Debt Securities	200	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	44	58
Available-for-sale debt securities, Due after five years through ten years, Amount	8	0
Available-for-sale debt securities, Due after ten years, Amount	$ 11,588	$ 10,333
Available-for-sale debt securities, Yield	2.80%	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	2.80%	0.00%
Available-for-sale debt securities, Due after ten years, Yield	2.80%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 11,704	$ 10,431
Available-for-sale Securities, Debt Securities	11,640	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	0	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	$ 457	$ 223
Available-for-sale debt securities, Yield	1.70%	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	0.00%	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	1.70%	1.40%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 458	$ 254
Available-for-sale Securities, Debt Securities	457	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	9	0
Available-for-sale debt securities, Due after one year through five years, Amount	1,224	1,311
Available-for-sale debt securities, Due after five years through ten years, Amount	605	463
Available-for-sale debt securities, Due after ten years, Amount	$ 217	$ 217
Available-for-sale debt securities, Yield	2.10%	1.90%
Available-for-sale debt securities, Due in one year or less, Yield	1.10%	0.00%
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	2.30%	2.00%
Available-for-sale debt securities, Due after ten years, Yield	2.30%	2.20%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,053	$ 1,989
Available-for-sale Securities, Debt Securities	2,055	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	28	33
Available-for-sale debt securities, Due after one year through five years, Amount	628	460
Available-for-sale debt securities, Due after five years through ten years, Amount	369	216
Available-for-sale debt securities, Due after ten years, Amount	$ 33	$ 37
Available-for-sale debt securities, Yield	2.90%	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	2.50%	2.70%
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.80%
Available-for-sale debt securities, Due after ten years, Yield	5.60%	5.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,054	$ 734
Available-for-sale Securities, Debt Securities	$ 1,058	$ 746