Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	$ 118	$ 0
Held-to-Maturity Debt Securities, Yield	3.20%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 118
Held-to-Maturity Securities, Due After Ten Years, Yield	3.20%
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 17,464	$ 16,440
Available-for-sale debt securities, Yield	2.90%	2.70%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 17,356	$ 16,542
Available-for-sale debt securities, Due in one year or less, Amount	$ 229	$ 157
Available-for-sale debt securities, Due in one year or less, Yield	2.20%	2.00%
Amortized cost of available-for-sale debt securities, Due in one year or less, Amount	$ 228	$ 156
Available-for-sale debt securities, Due after one year through five years, Amount	$ 2,175	$ 2,397
Available-for-sale debt securities, Due after one year through five years, Yield	2.40%	2.10%
Amortized cost of available-for-sale debt securities, Due after one year through five years, Amount	$ 2,167	$ 2,404
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 1,564	$ 2,424
Available-for-sale debt securities, Due after five years through ten years, Yield	2.90%	2.50%
Available-for-sale Securities, Debt Maturities, after Five Through Ten Years, Amortized Cost Basis	$ 1,539	$ 2,436
Available-for-sale debt securities, Due after ten years, Amount	$ 13,496	$ 11,462
Available-for-sale debt securities, Due after ten years, Yield	3.00%	2.90%
Amortized cost of available-for-sale debt securities, Due after ten years, Amount	$ 13,422	$ 11,546
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 356	$ 1,741
Available-for-sale debt securities, Yield	2.10%	1.80%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 345	$ 1,760
Available-for-sale debt securities, Due in one year or less, Amount	$ 8	$ 6
Available-for-sale debt securities, Due in one year or less, Yield	4.80%	5.10%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 91	$ 510
Available-for-sale debt securities, Due after one year through five years, Yield	1.60%	1.20%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 257	$ 1,225
Available-for-sale debt securities, Due after five years through ten years, Yield	2.20%	2.10%
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 743	$ 716
Available-for-sale debt securities, Yield	3.10%	3.20%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 721	$ 693
Available-for-sale debt securities, Due in one year or less, Amount	$ 150	$ 86
Available-for-sale debt securities, Due in one year or less, Yield	1.90%	1.30%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 44	$ 37
Available-for-sale debt securities, Due after one year through five years, Yield	1.70%	2.20%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 106	$ 141
Available-for-sale debt securities, Due after five years through ten years, Yield	3.10%	2.80%
Available-for-sale debt securities, Due after ten years, Amount	$ 443	$ 452
Available-for-sale debt securities, Due after ten years, Yield	3.60%	3.70%
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 191	$ 177
Available-for-sale debt securities, Yield	2.60%	2.60%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 181	$ 169
Available-for-sale debt securities, Due in one year or less, Amount	$ 10	$ 9
Available-for-sale debt securities, Due in one year or less, Yield	1.50%	1.90%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 74	$ 77
Available-for-sale debt securities, Due after one year through five years, Yield	2.90%	2.80%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 107	$ 91
Available-for-sale debt securities, Due after five years through ten years, Yield	2.50%	2.60%
Available-for-sale debt securities, Due after ten years, Amount	$ 0	$ 0
Available-for-sale debt securities, Due after ten years, Yield	0.00%	0.00%
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 12,313	$ 10,366
Available-for-sale debt securities, Yield	3.00%	2.90%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 12,241	$ 10,459
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
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, Amount	$ 1	$ 33
Available-for-sale debt securities, Due after one year through five years, Yield	4.50%	2.10%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 31	$ 36
Available-for-sale debt securities, Due after five years through ten years, Yield	2.50%	2.50%
Available-for-sale debt securities, Due after ten years, Amount	$ 12,281	$ 10,297
Available-for-sale debt securities, Due after ten years, Yield	3.00%	2.90%
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 500	$ 481
Available-for-sale debt securities, Yield	2.30%	2.00%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 515	$ 486
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 0
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, Amount	$ 0	$ 0
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, Amount	$ 3	$ 3
Available-for-sale debt securities, Due after five years through ten years, Yield	2.70%	2.70%
Available-for-sale debt securities, Due after ten years, Amount	$ 497	$ 478
Available-for-sale debt securities, Due after ten years, Yield	2.30%	2.00%
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,781	$ 1,755
Available-for-sale debt securities, Yield	2.50%	2.30%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,792	$ 1,762
Available-for-sale debt securities, Due in one year or less, Amount	$ 0	$ 6
Available-for-sale debt securities, Due in one year or less, Yield	0.00%	1.40%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 1,061	$ 1,027
Available-for-sale debt securities, Due after one year through five years, Yield	2.30%	2.10%
Available-for-sale debt securities, Due after five years through ten years, Amount	$ 479	$ 518
Available-for-sale debt securities, Due after five years through ten years, Yield	2.90%	2.60%
Available-for-sale debt securities, Due after ten years, Amount	$ 241	$ 204
Available-for-sale debt securities, Due after ten years, Yield	2.40%	2.20%
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	$ 1,580	$ 1,204
Available-for-sale debt securities, Yield	2.90%	2.90%
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,561	$ 1,213
Available-for-sale debt securities, Due in one year or less, Amount	$ 61	$ 50
Available-for-sale debt securities, Due in one year or less, Yield	2.90%	3.00%
Available-for-sale debt securities, Due after one year through five years, Amount	$ 904	$ 713
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, Amount	$ 581	$ 410
Available-for-sale debt securities, Due after five years through ten years, Yield	3.30%	3.40%
Available-for-sale debt securities, Due after ten years, Amount	$ 34	$ 31
Available-for-sale debt securities, Due after ten years, Yield	5.30%	5.40%