Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 29,225	$ 30,284
Cash equivalents	3,200	73
Held-to-maturity securities
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 1,390	$ 1,568
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	$ 14	$ 21
Debt securities, held-to-maturity, due after one year through five years, yield	2.40%	2.20%
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	$ 1,376	$ 1,547
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	$ 807	$ 2,048
Debt securities, available-for-sale, yield	1.20%	1.50%
Debt securities, available-for-sale, due in one year or less	$ 14	$ 65
Debt securities, available-for-sale, due in one year or less, yield	0.30%	2.10%
Debt securities, available-for-sale, due after one year through five years	$ 709	$ 1,590
Debt securities, available-for-sale, due after one year through five years, yield	1.10%	1.40%
Debt securities, available-for-sale, due after five years through ten years	$ 84	$ 393
Debt securities, available-for-sale, due after five years through ten years, yield	1.70%	1.70%
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	$ 784	$ 2,059
Available-for-sale securities | US States and political subdivisions
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 913	$ 641
Debt securities, available-for-sale, yield	3.20%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 20	$ 22
Debt securities, available-for-sale, due in one year or less, yield	2.50%	2.70%
Debt securities, available-for-sale, due after one year through five years	$ 88	$ 75
Debt securities, available-for-sale, due after one year through five years, yield	2.40%	2.30%
Debt securities, available-for-sale, due after five years through ten years	$ 176	$ 159
Debt securities, available-for-sale, due after five years through ten years, yield	2.90%	2.80%
Debt securities, available-for-sale, due after ten years	$ 629	$ 385
Debt securities, available-for-sale, due after ten years, yield	3.40%	3.40%
Debt securities, available-for-sale, amortized cost	$ 876	$ 623
Available-for-sale securities | Foreign government
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 162	$ 186
Debt securities, available-for-sale, yield	2.10%	1.90%
Debt securities, available-for-sale, due in one year or less	$ 8	$ 35
Debt securities, available-for-sale, due in one year or less, yield	1.70%	0.40%
Debt securities, available-for-sale, due after one year through five years	$ 79	$ 65
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	$ 75	$ 86
Debt securities, available-for-sale, due after five years through ten years, yield	2.00%	2.30%
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	$ 153	$ 184
Available-for-sale securities | Agency mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 19,884	$ 21,404
Debt securities, available-for-sale, yield	3.20%	3.20%
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	$ 44	$ 47
Debt securities, available-for-sale, due after five years through ten years, yield	2.00%	2.00%
Debt securities, available-for-sale, due after ten years	$ 19,840	$ 21,357
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.20%
Debt securities, available-for-sale, amortized cost	$ 19,136	$ 21,183
Available-for-sale securities | Mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 3,425	$ 2,850
Debt securities, available-for-sale, yield	3.20%	3.20%
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	$ 3,425	$ 2,850
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.20%
Debt securities, available-for-sale, amortized cost	$ 3,387	$ 2,841
Available-for-sale securities | Agency mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,786	$ 1,382
Debt securities, available-for-sale, yield	2.50%	2.90%
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	3.30%	3.20%
Debt securities, available-for-sale, due after five years through ten years	$ 1,247	$ 1,109
Debt securities, available-for-sale, due after five years through ten years, yield	2.60%	3.00%
Debt securities, available-for-sale, due after ten years	$ 536	$ 270
Debt securities, available-for-sale, due after ten years, yield	2.20%	2.40%
Debt securities, available-for-sale, amortized cost	$ 1,647	$ 1,344
Available-for-sale securities | Mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 38	$ 42
Debt securities, available-for-sale, yield	3.60%	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	$ 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	$ 38	$ 42
Debt securities, available-for-sale, due after ten years, yield	3.60%	3.50%
Debt securities, available-for-sale, amortized cost	$ 41	$ 41
Available-for-sale securities | Asset-backed
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 356	$ 368
Debt securities, available-for-sale, yield	3.40%	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	$ 294	$ 317
Debt securities, available-for-sale, due after one year through five years, yield	3.50%	3.60%
Debt securities, available-for-sale, due after five years through ten years	$ 28	$ 5
Debt securities, available-for-sale, due after five years through ten years, yield	2.60%	2.70%
Debt securities, available-for-sale, due after ten years	$ 34	$ 46
Debt securities, available-for-sale, due after ten years, yield	3.10%	3.00%
Debt securities, available-for-sale, amortized cost	$ 352	$ 365
Available-for-sale securities | Corporate debt
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,854	$ 1,363
Debt securities, available-for-sale, yield	3.00%	3.20%
Debt securities, available-for-sale, due in one year or less	$ 153	$ 125
Debt securities, available-for-sale, due in one year or less, yield	2.90%	2.90%
Debt securities, available-for-sale, due after one year through five years	$ 705	$ 580
Debt securities, available-for-sale, due after one year through five years, yield	2.90%	3.00%
Debt securities, available-for-sale, due after five years through ten years	$ 973	$ 649
Debt securities, available-for-sale, due after five years through ten years, yield	3.10%	3.40%
Debt securities, available-for-sale, due after ten years	$ 23	$ 9
Debt securities, available-for-sale, due after ten years, yield	2.40%	3.30%
Debt securities, available-for-sale, amortized cost	$ 1,761	$ 1,327
Available-for-sale securities | Available-for-sale debt securities
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 29,225	$ 30,284
Debt securities, available-for-sale, yield	3.10%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 195	$ 247
Debt securities, available-for-sale, due in one year or less, yield	2.60%	2.30%
Debt securities, available-for-sale, due after one year through five years	$ 1,878	$ 2,630
Debt securities, available-for-sale, due after one year through five years, yield	2.30%	2.10%
Debt securities, available-for-sale, due after five years through ten years	$ 2,627	$ 2,448
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	$ 24,525	$ 24,959
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.20%
Debt securities, available-for-sale, amortized cost	$ 28,137	$ 29,967
Debt securities, available-for-sale, maturity, within one year, amortized cost	193	246
Debt securities, available-for-sale, maturity, after one through five years, amortized cost	1,821	2,624
Debt securities, available-for-sale, maturity, after five through ten years, amortized cost	2,431	2,378
Debt securities, available-for-sale, maturity, after ten years, amortized cost	23,692	24,719
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	$ 1,376	$ 1,547
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	$ 1,376	$ 1,547
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	$ 14	$ 21
Debt securities, held-to-maturity, yield	2.40%	2.20%
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	$ 14	$ 21
Debt securities, held-to-maturity, due after one year through five years, yield	2.40%	2.20%
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	$ 0	$ 0
Debt securities, held-to-maturity, due after ten years, yield	0.00%	0.00%