Investment Securities (Contractual Maturity of Securities) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Debt Securities [Line Items]
Document Period End Date	Sep. 30, 2020
Available for Sale Securities, Amortized Cost, 1 year or less	$ 4,828
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	14,447
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	8,595
Available for Sale Securities, Amortized Cost, After 10 years	58,474
Securities available for sale debt securities, amortized cost	86,344	$ 67,790
Available-for-sale Securities, Fair value, 1 year or less	4,848
Available-for-sale Securities, Fair value, After 1 year through 5 years	15,081
Available-for-sale Securities, Fair value, After 5 years through 10 years	9,048
Available-for-sale Securities, Fair value, After 10 years	60,770
Available-for-sale Securities, Fair value, Total	$ 89,747	69,163
Weighted-average yield, GAAP basis, available for sale securities	2.62%
Held to Maturity Securities, Amortized Cost, 1 year or less	$ 14
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	636
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	421
Held to Maturity Securities, Amortized Cost, After 10 years	367
Held to maturity securities, amortized cost	1,438	17,661
Held-to-maturity Securities, Fair Value, 1 year or less	14
Held-to-maturity Securities, Fair Value, After 1 year through 5 years	677
Held-to-maturity Securities, Fair Value, After 5 years through 10 years	513
Held-to-maturity Securities, Fair Value, After 10 years	410
Held-to-maturity Securities, Debt Maturities, Fair Value, Total	$ 1,614	$ 18,044
Weighted-average yield, GAAP basis, held to maturity securities	3.29%
One Year or Less [Member]
Debt Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	1.10%
Weighted-average yield, GAAP basis, held to maturity securities	2.93%
After One Year Through Five Years [Member]
Debt Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.08%
Weighted-average yield, GAAP basis, held to maturity securities	3.28%
After Five Years Through Ten Years [Member]
Debt Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.05%
Weighted-average yield, GAAP basis, held to maturity securities	3.93%
After Ten Years [Member]
Debt Securities [Line Items]
Weighted-average yield, GAAP basis, available for sale securities	2.92%
Weighted-average yield, GAAP basis, held to maturity securities	2.48%
US Treasury and Government [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	$ 3,891
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	9,478
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	2,979
Available for Sale Securities, Amortized Cost, After 10 years	925
Securities available for sale debt securities, amortized cost	17,273
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	199
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	309
Held to Maturity Securities, Amortized Cost, After 10 years	282
Held to maturity securities, amortized cost	790
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	1
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	155
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	2,098
Available for Sale Securities, Amortized Cost, After 10 years	48,948
Securities available for sale debt securities, amortized cost	51,202
Residential Mortgage-backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, After 10 years	1,376
Securities available for sale debt securities, amortized cost	1,376
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Agency [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	21
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	609
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	663
Available for Sale Securities, Amortized Cost, After 10 years	1,531
Securities available for sale debt securities, amortized cost	2,824
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities Non-agency [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	83
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	247
Available for Sale Securities, Amortized Cost, After 10 years	3,521
Securities available for sale debt securities, amortized cost	3,851
Asset backed [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	26
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	2,625
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	1,316
Available for Sale Securities, Amortized Cost, After 10 years	1,191
Securities available for sale debt securities, amortized cost	5,158
Other [Member]
Debt Securities [Line Items]
Available for Sale Securities, Amortized Cost, 1 year or less	889
Available for Sale Securities, Amortized Cost, After 1 year through 5 years	1,497
Available for Sale Securities, Amortized Cost, After 5 years through 10 years	1,292
Available for Sale Securities, Amortized Cost, After 10 years	982
Securities available for sale debt securities, amortized cost	4,660
Held to Maturity Securities, Amortized Cost, 1 year or less	14
Held to Maturity Securities, Amortized Cost, After 1 year through 5 years	437
Held to Maturity Securities, Amortized Cost, After 5 years through 10 years	112
Held to Maturity Securities, Amortized Cost, After 10 years	85
Held to maturity securities, amortized cost	$ 648