Investment Securities (Investments Classified by Contractual Maturity Date) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 33,446	$ 29,830
Cash equivalents	20	25
Held-to-maturity securities
Schedule of Investments [Line Items]
Debt securities, held-to-maturity, amortized cost, before other-than-temporary impairment	$ 1,197	$ 1,253
Debt securities, held-to-maturity, yield	3.00%	3.00%
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	$ 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	$ 1,197	$ 1,253
Debt securities, held-to-maturity, due after ten years, yield	3.00%	3.00%
Available-for-sale securities \| US Treasury
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,706	$ 803
Debt securities, available-for-sale, yield	1.10%	1.20%
Debt securities, available-for-sale, due in one year or less	$ 12	$ 13
Debt securities, available-for-sale, due in one year or less, yield	0.10%	0.10%
Debt securities, available-for-sale, due after one year through five years	$ 495	$ 708
Debt securities, available-for-sale, due after one year through five years, yield	1.00%	1.10%
Debt securities, available-for-sale, due after five years through ten years	$ 1,199	$ 82
Debt securities, available-for-sale, due after five years through ten years, yield	1.10%	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	$ 1,743	$ 783
Available-for-sale securities \| US States and political subdivisions
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 1,064	$ 1,095
Debt securities, available-for-sale, yield	3.00%	3.00%
Debt securities, available-for-sale, due in one year or less	$ 44	$ 49
Debt securities, available-for-sale, due in one year or less, yield	1.50%	1.40%
Debt securities, available-for-sale, due after one year through five years	$ 106	$ 103
Debt securities, available-for-sale, due after one year through five years, yield	2.50%	2.30%
Debt securities, available-for-sale, due after five years through ten years	$ 227	$ 228
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	$ 687	$ 715
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.30%
Debt securities, available-for-sale, amortized cost	$ 1,031	$ 1,046
Available-for-sale securities \| Foreign government
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 172	$ 176
Debt securities, available-for-sale, yield	1.90%	2.10%
Debt securities, available-for-sale, due in one year or less	$ 14	$ 9
Debt securities, available-for-sale, due in one year or less, yield	1.80%	1.70%
Debt securities, available-for-sale, due after one year through five years	$ 94	$ 86
Debt securities, available-for-sale, due after one year through five years, yield	1.90%	2.30%
Debt securities, available-for-sale, due after five years through ten years	$ 64	$ 81
Debt securities, available-for-sale, due after five years through ten years, yield	1.90%	1.90%
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	$ 169	$ 167
Available-for-sale securities \| Agency mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 21,518	$ 18,588
Debt securities, available-for-sale, yield	2.70%	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	$ 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	$ 33	$ 37
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	$ 21,485	$ 18,551
Debt securities, available-for-sale, due after ten years, yield	2.70%	3.10%
Debt securities, available-for-sale, amortized cost	$ 21,346	$ 18,053
Available-for-sale securities \| Mortgage-backed residential
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 2,312	$ 2,640
Debt securities, available-for-sale, yield	3.00%	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	$ 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	$ 32	$ 36
Debt securities, available-for-sale, due after five years through ten years, yield	2.90%	2.90%
Debt securities, available-for-sale, due after ten years	$ 2,280	$ 2,604
Debt securities, available-for-sale, due after ten years, yield	3.00%	3.10%
Debt securities, available-for-sale, amortized cost	$ 2,284	$ 2,595
Available-for-sale securities \| Agency mortgage-backed commercial
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 4,152	$ 4,189
Debt securities, available-for-sale, yield	1.90%	1.90%
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	$ 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	$ 1,675	$ 1,628
Debt securities, available-for-sale, due after five years through ten years, yield	2.30%	2.30%
Debt securities, available-for-sale, due after ten years	$ 2,477	$ 2,561
Debt securities, available-for-sale, due after ten years, yield	1.70%	1.70%
Debt securities, available-for-sale, amortized cost	$ 4,272	$ 4,063
Available-for-sale securities \| Asset-backed
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 474	$ 425
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	$ 338	$ 349
Debt securities, available-for-sale, due after one year through five years, yield	2.80%	3.00%
Debt securities, available-for-sale, due after five years through ten years	$ 111	$ 49
Debt securities, available-for-sale, due after five years through ten years, yield	1.30%	1.80%
Debt securities, available-for-sale, due after ten years	$ 25	$ 27
Debt securities, available-for-sale, due after ten years, yield	3.20%	3.10%
Debt securities, available-for-sale, amortized cost	$ 470	$ 420
Available-for-sale securities \| Corporate debt
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 2,048	$ 1,914
Debt securities, available-for-sale, yield	2.40%	2.70%
Debt securities, available-for-sale, due in one year or less	$ 127	$ 155
Debt securities, available-for-sale, due in one year or less, yield	2.80%	2.70%
Debt securities, available-for-sale, due after one year through five years	$ 804	$ 625
Debt securities, available-for-sale, due after one year through five years, yield	2.50%	2.90%
Debt securities, available-for-sale, due after five years through ten years	$ 1,097	$ 1,077
Debt securities, available-for-sale, due after five years through ten years, yield	2.40%	2.60%
Debt securities, available-for-sale, due after ten years	$ 20	$ 57
Debt securities, available-for-sale, due after ten years, yield	2.30%	2.10%
Debt securities, available-for-sale, amortized cost	$ 2,021	$ 1,809
Available-for-sale securities \| Available-for-sale debt securities
Schedule of Investments [Line Items]
Total available-for-sale debt securities	$ 33,446	$ 29,830
Debt securities, available-for-sale, yield	2.50%	2.80%
Debt securities, available-for-sale, due in one year or less	$ 197	$ 226
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	$ 1,837	$ 1,871
Debt securities, available-for-sale, due after one year through five years, yield	2.10%	2.20%
Debt securities, available-for-sale, due after five years through ten years	$ 4,438	$ 3,218
Debt securities, available-for-sale, due after five years through ten years, yield	2.00%	2.40%
Debt securities, available-for-sale, due after ten years	$ 26,974	$ 24,515
Debt securities, available-for-sale, due after ten years, yield	2.60%	3.00%
Debt securities, available-for-sale, amortized cost	$ 33,336	$ 28,936
Debt securities, available-for-sale, maturity, within one year, amortized cost	195	224
Debt securities, available-for-sale, maturity, after one through five years, amortized cost	1,797	1,808
Debt securities, available-for-sale, maturity, after five through ten years, amortized cost	4,423	3,022
Debt securities, available-for-sale, maturity, after ten years, amortized cost	26,921	23,882
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	$ 1,197	$ 1,253
Debt securities, held-to-maturity, yield	3.00%	3.00%
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	$ 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	$ 1,197	$ 1,253
Debt securities, held-to-maturity, due after ten years, yield	3.00%	3.00%

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Weighted average yield of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), maturing after tenth rolling fiscal year following latest fiscal year. For interim and annual periods when interim period is reported on rolling approach, from latest statement of financial position date.

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