Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Sep. 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	$ 121	$ 108
Available-for-sale debt securities, Due after one year through five years, Amount	2,863	2,676
Available-for-sale debt securities, Due after five years through ten years, Amount	2,084	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	120	108
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	2,854	2,674
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	2,067	1,374
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	$ 12,644	$ 11,060
Available-for-sale debt securities, Yield	2.60%	2.50%
Available-for-sale debt securities, Due in one year or less, Yield	2.60%	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	2.50%	2.40%
Available-for-sale debt securities, Due after ten years, Yield	2.80%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 17,685	$ 15,216
Available-for-sale Securities, Debt Securities	17,773	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	7	7
Available-for-sale debt securities, Due after one year through five years, Amount	905	677
Available-for-sale debt securities, Due after five years through ten years, Amount	897	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	5.00%	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	2.10%	1.90%
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,805	$ 1,195
Available-for-sale Securities, Debt Securities	1,809	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	53	34
Available-for-sale debt securities, Due after one year through five years, Amount	48	12
Available-for-sale debt securities, Due after five years through ten years, Amount	130	106
Available-for-sale debt securities, Due after ten years, Amount	$ 420	$ 254
Available-for-sale debt securities, Yield	3.30%	3.70%
Available-for-sale debt securities, Due in one year or less, Yield	2.20%	1.90%
Available-for-sale debt securities, Due after one year through five years, Yield	2.20%	2.10%
Available-for-sale debt securities, Due after five years through ten years, Yield	2.90%	3.00%
Available-for-sale debt securities, Due after ten years, Yield	3.70%	4.30%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 635	$ 389
Available-for-sale Securities, Debt Securities	651	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	9	0
Available-for-sale debt securities, Due after one year through five years, Amount	82	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	2.60%	2.70%
Available-for-sale debt securities, Due in one year or less, Yield	1.40%	0.00%
Available-for-sale debt securities, Due after one year through five years, Yield	2.70%	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	$ 176	$ 224
Available-for-sale Securities, Debt Securities	184	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	38	58
Available-for-sale debt securities, Due after five years through ten years, Amount	40	0
Available-for-sale debt securities, Due after ten years, Amount	$ 11,536	$ 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	2.50%	0.00%
Available-for-sale debt securities, Due after ten years, Yield	2.80%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 11,560	$ 10,431
Available-for-sale Securities, Debt Securities	11,614	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	3	0
Available-for-sale debt securities, Due after ten years, Amount	$ 514	$ 223
Available-for-sale debt securities, Yield	1.90%	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	2.70%	0.00%
Available-for-sale debt securities, Due after ten years, Yield	1.90%	1.40%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 519	$ 254
Available-for-sale Securities, Debt Securities	517	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	4	0
Available-for-sale debt securities, Due after one year through five years, Amount	1,189	1,311
Available-for-sale debt securities, Due after five years through ten years, Amount	553	463
Available-for-sale debt securities, Due after ten years, Amount	$ 205	$ 217
Available-for-sale debt securities, Yield	2.10%	1.90%
Available-for-sale debt securities, Due in one year or less, Yield	1.40%	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	2.40%	2.00%
Available-for-sale debt securities, Due after ten years, Yield	2.20%	2.20%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,947	$ 1,989
Available-for-sale Securities, Debt Securities	1,951	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	48	33
Available-for-sale debt securities, Due after one year through five years, Amount	601	460
Available-for-sale debt securities, Due after five years through ten years, Amount	368	216
Available-for-sale debt securities, Due after ten years, Amount	$ 30	$ 37
Available-for-sale debt securities, Yield	2.90%	3.20%
Available-for-sale debt securities, Due in one year or less, Yield	3.10%	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	5.50%	5.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,043	$ 734
Available-for-sale Securities, Debt Securities	$ 1,047	$ 746