Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 29,830	$ 30,284
Cash equivalents	25	73
Held-to-maturity securities
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 1,253	$ 1,568
Debt securities, held-to-maturity, yield	3.00%	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	$ 21
Debt securities, held-to-maturity, due after one year through five years, yield	0.00%	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	$ 1,253	$ 1,547
Debt securities, held-to-maturity, due after ten years, yield	3.00%	3.20%
Available-for-sale securities | US Treasury
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 803	$ 2,048
Debt securities, available-for-sale, yield	1.20%	1.50%
Debt securities, available-for-sale, due in one year or less	$ 13	$ 65
Debt securities, available-for-sale, due in one year or less, yield	0.10%	2.10%
Debt securities, available-for-sale, due after one year through five years	$ 708	$ 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	$ 82	$ 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	$ 783	$ 2,059
Available-for-sale securities | US States and political subdivisions
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,095	$ 641
Debt securities, available-for-sale, yield	3.00%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 49	$ 22
Debt securities, available-for-sale, due in one year or less, yield	1.40%	2.70%
Debt securities, available-for-sale, due after one year through five years	$ 103	$ 75
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	$ 228	$ 159
Debt securities, available-for-sale, due after five years through ten years, yield	2.70%	2.80%
Debt securities, available-for-sale, due after ten years	$ 715	$ 385
Debt securities, available-for-sale, due after ten years, yield	3.30%	3.40%
Debt securities, available-for-sale, amortized cost	$ 1,046	$ 623
Available-for-sale securities | Foreign government
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 176	$ 186
Debt securities, available-for-sale, yield	2.10%	1.90%
Debt securities, available-for-sale, due in one year or less	$ 9	$ 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	$ 86	$ 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	$ 81	$ 86
Debt securities, available-for-sale, due after five years through ten years, yield	1.90%	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	$ 167	$ 184
Available-for-sale securities | Agency mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 18,588	$ 21,404
Debt securities, available-for-sale, yield	3.10%	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	$ 37	$ 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	$ 18,551	$ 21,357
Debt securities, available-for-sale, due after ten years, yield	3.10%	3.20%
Debt securities, available-for-sale, amortized cost	$ 18,053	$ 21,183
Available-for-sale securities | Mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 2,640	$ 2,850
Debt securities, available-for-sale, yield	3.10%	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	$ 36	$ 0
Debt securities, available-for-sale, due after five years through ten years, yield	2.90%	0.00%
Debt securities, available-for-sale, due after ten years	$ 2,604	$ 2,850
Debt securities, available-for-sale, due after ten years, yield	3.10%	3.20%
Debt securities, available-for-sale, amortized cost	$ 2,595	$ 2,841
Available-for-sale securities | Agency mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 4,189	$ 1,382
Debt securities, available-for-sale, yield	1.90%	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	$ 0	$ 3
Debt securities, available-for-sale, due after one year through five years, yield	0.00%	3.20%
Debt securities, available-for-sale, due after five years through ten years	$ 1,628	$ 1,109
Debt securities, available-for-sale, due after five years through ten years, yield	2.30%	3.00%
Debt securities, available-for-sale, due after ten years	$ 2,561	$ 270
Debt securities, available-for-sale, due after ten years, yield	1.70%	2.40%
Debt securities, available-for-sale, amortized cost	$ 4,063	$ 1,344
Available-for-sale securities | Mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	0	$ 42
Debt securities, available-for-sale, yield		3.50%
Debt securities, available-for-sale, due in one year or less		$ 0
Debt securities, available-for-sale, due in one year or less, yield		0.00%
Debt securities, available-for-sale, due after one year through five years		$ 0
Debt securities, available-for-sale, due after one year through five years, yield		0.00%
Debt securities, available-for-sale, due after five years through ten years		$ 0
Debt securities, available-for-sale, due after five years through ten years, yield		0.00%
Debt securities, available-for-sale, due after ten years		$ 42
Debt securities, available-for-sale, due after ten years, yield		3.50%
Debt securities, available-for-sale, amortized cost	0	$ 41
Available-for-sale securities | Asset-backed
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 425	$ 368
Debt securities, available-for-sale, yield	2.90%	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	$ 349	$ 317
Debt securities, available-for-sale, due after one year through five years, yield	3.00%	3.60%
Debt securities, available-for-sale, due after five years through ten years	$ 49	$ 5
Debt securities, available-for-sale, due after five years through ten years, yield	1.80%	2.70%
Debt securities, available-for-sale, due after ten years	$ 27	$ 46
Debt securities, available-for-sale, due after ten years, yield	3.10%	3.00%
Debt securities, available-for-sale, amortized cost	$ 420	$ 365
Available-for-sale securities | Corporate debt
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,914	$ 1,363
Debt securities, available-for-sale, yield	2.70%	3.20%
Debt securities, available-for-sale, due in one year or less	$ 155	$ 125
Debt securities, available-for-sale, due in one year or less, yield	2.70%	2.90%
Debt securities, available-for-sale, due after one year through five years	$ 625	$ 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	$ 1,077	$ 649
Debt securities, available-for-sale, due after five years through ten years, yield	2.60%	3.40%
Debt securities, available-for-sale, due after ten years	$ 57	$ 9
Debt securities, available-for-sale, due after ten years, yield	2.10%	3.30%
Debt securities, available-for-sale, amortized cost	$ 1,809	$ 1,327
Available-for-sale securities | Available-for-sale debt securities
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 29,830	$ 30,284
Debt securities, available-for-sale, yield	2.80%	3.10%
Debt securities, available-for-sale, due in one year or less	$ 226	$ 247
Debt securities, available-for-sale, due in one year or less, yield	2.30%	2.30%
Debt securities, available-for-sale, due after one year through five years	$ 1,871	$ 2,630
Debt securities, available-for-sale, due after one year through five years, yield	2.20%	2.10%
Debt securities, available-for-sale, due after five years through ten years	$ 3,218	$ 2,448
Debt securities, available-for-sale, due after five years through ten years, yield	2.40%	2.80%
Debt securities, available-for-sale, due after ten years	$ 24,515	$ 24,959
Debt securities, available-for-sale, due after ten years, yield	3.00%	3.20%
Debt securities, available-for-sale, amortized cost	$ 28,936	$ 29,967
Debt securities, available-for-sale, maturity, within one year, amortized cost	224	246
Debt securities, available-for-sale, maturity, after one through five years, amortized cost	1,808	2,624
Debt securities, available-for-sale, maturity, after five through ten years, amortized cost	3,022	2,378
Debt securities, available-for-sale, maturity, after ten years, amortized cost	23,882	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	$ 1,253	$ 1,547
Debt securities, held-to-maturity, yield	3.00%	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	$ 1,253	$ 1,547
Debt securities, held-to-maturity, due after ten years, yield	3.00%	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
Debt securities, held-to-maturity, yield		2.20%
Debt securities, held-to-maturity, maturity, within one year, amortized Cost		$ 0
Debt securities, held-to-maturity, due in one year or less, yield		0.00%
Debt securities, held-to-maturity, maturity, one through five years, amortized Cost		$ 21
Debt securities, held-to-maturity, due after one year through five years, yield		2.20%
Debt securities, held-to-maturity, maturity, after five through ten years, amortized cost		$ 0
Debt securities, held-to-maturity, due after five years through ten years, yield		0.00%
Debt securities, held-to-maturity, maturity, after 10 Years, amortized cost		$ 0
Debt securities, held-to-maturity, due after ten years, yield		0.00%