Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 30,284	$ 25,303
Cash equivalents	73	35
Held-to-maturity securities
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 1,568	$ 2,362
Debt securities, held-to-maturity, yield	3.20%	3.20%
Debt securities, held-to-maturity, maturity, within one year, amortized Cost	$ 0	$ 0
Debt securities, held-to-maturity, due in one year or less, yield	0.00%	0.00%
Debt securities, held-to-maturity, maturity, one through five years, amortized Cost	$ 21	$ 42
Debt securities, held-to-maturity, due after one year through five years, yield	2.20%	2.00%
Debt securities, held-to-maturity, maturity, after five through ten years, amortized cost	$ 0	$ 1
Debt securities, held-to-maturity, due after five years through ten years, yield	0.00%	3.30%
Debt securities, held-to-maturity, maturity, after 10 Years, amortized cost	$ 1,547	$ 2,319
Debt securities, held-to-maturity, due after ten years, yield	3.20%	3.20%
Available-for-sale securities | US Treasury
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 2,048	$ 1,851
Debt securities, available-for-sale, yield	1.50%	1.90%
Debt securities, available-for-sale, due in one year or less	$ 65	$ 12
Debt securities, available-for-sale, due in one year or less, yield	2.10%	1.00%
Debt securities, available-for-sale, due after one year through five years	$ 1,590	$ 1,277
Debt securities, available-for-sale, due after one year through five years, yield	1.40%	1.80%
Debt securities, available-for-sale, due after five years through ten years	$ 393	$ 562
Debt securities, available-for-sale, due after five years through ten years, yield	1.70%	2.00%
Debt securities, available-for-sale, due after ten years	$ 0	$ 0
Debt securities, available-for-sale, due after ten years, yield	0.00%	0.00%
Debt securities, available-for-sale, amortized cost	$ 2,059	$ 1,911
Available-for-sale securities | US States and political subdivisions
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 641	$ 802
Debt securities, available-for-sale, yield	3.10%	3.00%
Debt securities, available-for-sale, due in one year or less	$ 22	$ 49
Debt securities, available-for-sale, due in one year or less, yield	2.70%	1.90%
Debt securities, available-for-sale, due after one year through five years	$ 75	$ 43
Debt securities, available-for-sale, due after one year through five years, yield	2.30%	2.30%
Debt securities, available-for-sale, due after five years through ten years	$ 159	$ 252
Debt securities, available-for-sale, due after five years through ten years, yield	2.80%	2.60%
Debt securities, available-for-sale, due after ten years	$ 385	$ 458
Debt securities, available-for-sale, due after ten years, yield	3.40%	3.40%
Debt securities, available-for-sale, amortized cost	$ 623	$ 816
Available-for-sale securities | Foreign government
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 186	$ 145
Debt securities, available-for-sale, yield	1.90%	2.40%
Debt securities, available-for-sale, due in one year or less	$ 35	$ 18
Debt securities, available-for-sale, due in one year or less, yield	0.40%	3.10%
Debt securities, available-for-sale, due after one year through five years	$ 65	$ 60
Debt securities, available-for-sale, due after one year through five years, yield	2.30%	2.30%
Debt securities, available-for-sale, due after five years through ten years	$ 86	$ 67
Debt securities, available-for-sale, due after five years through ten years, yield	2.30%	2.40%
Debt securities, available-for-sale, due after ten years	$ 0	$ 0
Debt securities, available-for-sale, due after ten years, yield	0.00%	0.00%
Debt securities, available-for-sale, amortized cost	$ 184	$ 145
Available-for-sale securities | Agency mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 21,404	$ 17,138
Debt securities, available-for-sale, yield	3.20%	3.30%
Debt securities, available-for-sale, due in one year or less	$ 0	$ 0
Debt securities, available-for-sale, due in one year or less, yield	0.00%	0.00%
Debt securities, available-for-sale, due after one year through five years	$ 0	$ 0
Debt securities, available-for-sale, due after one year through five years, yield	0.00%	0.00%
Debt securities, available-for-sale, due after five years through ten years	$ 47	$ 54
Debt securities, available-for-sale, due after five years through ten years, yield	2.00%	1.90%
Debt securities, available-for-sale, due after ten years	$ 21,357	$ 17,084
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.30%
Debt securities, available-for-sale, amortized cost	$ 21,183	$ 17,486
Available-for-sale securities | Mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 2,850	$ 2,686
Debt securities, available-for-sale, yield	3.20%	3.30%
Debt securities, available-for-sale, due in one year or less	$ 0	$ 0
Debt securities, available-for-sale, due in one year or less, yield	0.00%	0.00%
Debt securities, available-for-sale, due after one year through five years	$ 0	$ 0
Debt securities, available-for-sale, due after one year through five years, yield	0.00%	0.00%
Debt securities, available-for-sale, due after five years through ten years	$ 0	$ 0
Debt securities, available-for-sale, due after five years through ten years, yield	0.00%	0.00%
Debt securities, available-for-sale, due after ten years	$ 2,850	$ 2,686
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.30%
Debt securities, available-for-sale, amortized cost	$ 2,841	$ 2,796
Available-for-sale securities | Agency mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,382	$ 3
Debt securities, available-for-sale, yield	2.90%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 0	$ 0
Debt securities, available-for-sale, due in one year or less, yield	0.00%	0.00%
Debt securities, available-for-sale, due after one year through five years	$ 3	$ 3
Debt securities, available-for-sale, due after one year through five years, yield	3.20%	3.10%
Debt securities, available-for-sale, due after five years through ten years	$ 1,109	$ 0
Debt securities, available-for-sale, due after five years through ten years, yield	3.00%	0.00%
Debt securities, available-for-sale, due after ten years	$ 270	$ 0
Debt securities, available-for-sale, due after ten years, yield	2.40%	0.00%
Debt securities, available-for-sale, amortized cost	$ 1,344	$ 3
Available-for-sale securities | Mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 42	$ 714
Debt securities, available-for-sale, yield	3.50%	3.80%
Debt securities, available-for-sale, due in one year or less	$ 0	$ 0
Debt securities, available-for-sale, due in one year or less, yield	0.00%	0.00%
Debt securities, available-for-sale, due after one year through five years	$ 0	$ 0
Debt securities, available-for-sale, due after one year through five years, yield	0.00%	0.00%
Debt securities, available-for-sale, due after five years through ten years	$ 0	$ 46
Debt securities, available-for-sale, due after five years through ten years, yield	0.00%	3.90%
Debt securities, available-for-sale, due after ten years	$ 42	$ 668
Debt securities, available-for-sale, due after ten years, yield	3.50%	3.80%
Debt securities, available-for-sale, amortized cost	$ 41	$ 715
Available-for-sale securities | Asset-backed
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 368	$ 723
Debt securities, available-for-sale, yield	3.50%	3.50%
Debt securities, available-for-sale, due in one year or less	$ 0	$ 0
Debt securities, available-for-sale, due in one year or less, yield	0.00%	0.00%
Debt securities, available-for-sale, due after one year through five years	$ 317	$ 478
Debt securities, available-for-sale, due after one year through five years, yield	3.60%	3.40%
Debt securities, available-for-sale, due after five years through ten years	$ 5	$ 121
Debt securities, available-for-sale, due after five years through ten years, yield	2.70%	4.00%
Debt securities, available-for-sale, due after ten years	$ 46	$ 124
Debt securities, available-for-sale, due after ten years, yield	3.00%	3.30%
Debt securities, available-for-sale, amortized cost	$ 365	$ 723
Available-for-sale securities | Corporate debt
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,363	$ 1,241
Debt securities, available-for-sale, yield	3.20%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 125	$ 144
Debt securities, available-for-sale, due in one year or less, yield	2.90%	2.80%
Debt securities, available-for-sale, due after one year through five years	$ 580	$ 496
Debt securities, available-for-sale, due after one year through five years, yield	3.00%	2.90%
Debt securities, available-for-sale, due after five years through ten years	$ 649	$ 581
Debt securities, available-for-sale, due after five years through ten years, yield	3.40%	3.30%
Debt securities, available-for-sale, due after ten years	$ 9	$ 20
Debt securities, available-for-sale, due after ten years, yield	3.30%	5.50%
Debt securities, available-for-sale, amortized cost	$ 1,327	$ 1,286
Available-for-sale securities | Available-for-sale debt securities
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 30,284	$ 25,303
Debt securities, available-for-sale, yield	3.10%	3.20%
Debt securities, available-for-sale, due in one year or less	$ 247	$ 223
Debt securities, available-for-sale, due in one year or less, yield	2.30%	2.60%
Debt securities, available-for-sale, due after one year through five years	$ 2,630	$ 2,357
Debt securities, available-for-sale, due after one year through five years, yield	2.10%	2.40%
Debt securities, available-for-sale, due after five years through ten years	$ 2,448	$ 1,683
Debt securities, available-for-sale, due after five years through ten years, yield	2.80%	2.80%
Debt securities, available-for-sale, due after ten years	$ 24,959	$ 21,040
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.30%
Debt securities, available-for-sale, amortized cost	$ 29,967	$ 25,881
Debt securities, available-for-sale, maturity, within one year, amortized cost	246	224
Debt securities, available-for-sale, maturity, after one through five years, amortized cost	2,624	2,405
Debt securities, available-for-sale, maturity, after five through ten years, amortized cost	2,378	1,743
Debt securities, available-for-sale, maturity, after ten years, amortized cost	24,719	21,509
Held-to-maturity securities | Agency mortgage-backed residential
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 1,547	$ 2,319
Debt securities, held-to-maturity, yield	3.20%	3.20%
Debt securities, held-to-maturity, maturity, within one year, amortized Cost	$ 0	$ 0
Debt securities, held-to-maturity, due in one year or less, yield	0.00%	0.00%
Debt securities, held-to-maturity, maturity, one through five years, amortized Cost	$ 0	$ 0
Debt securities, held-to-maturity, due after one year through five years, yield	0.00%	0.00%
Debt securities, held-to-maturity, maturity, after five through ten years, amortized cost	$ 0	$ 0
Debt securities, held-to-maturity, due after five years through ten years, yield	0.00%	0.00%
Debt securities, held-to-maturity, maturity, after 10 Years, amortized cost	$ 1,547	$ 2,319
Debt securities, held-to-maturity, due after ten years, yield	3.20%	3.20%
Held-to-maturity securities | Asset-backed
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 21	$ 43
Debt securities, held-to-maturity, yield	2.20%	2.00%
Debt securities, held-to-maturity, maturity, within one year, amortized Cost	$ 0	$ 0
Debt securities, held-to-maturity, due in one year or less, yield	0.00%	0.00%
Debt securities, held-to-maturity, maturity, one through five years, amortized Cost	$ 21	$ 42
Debt securities, held-to-maturity, due after one year through five years, yield	2.20%	2.00%
Debt securities, held-to-maturity, maturity, after five through ten years, amortized cost	$ 0	$ 1
Debt securities, held-to-maturity, due after five years through ten years, yield	0.00%	3.30%
Debt securities, held-to-maturity, maturity, after 10 Years, amortized cost	$ 0	$ 0
Debt securities, held-to-maturity, due after ten years, yield	0.00%	0.00%