Investment Securities (Narrative) (Details) - USD ($)			3 Months Ended	12 Months Ended
		Jan. 01, 2019	Mar. 31, 2019	Dec. 31, 2020		Dec. 31, 2019		Dec. 31, 2018	Jan. 01, 2020
Schedule of Held-to-maturity Securities [Line Items]
Other comprehensive income (loss), net of tax				$ 5,306,000,000		$ 340,000,000		$ (67,000,000)
Assets	[1]			549,009,000,000		294,005,000,000
Held to maturity securities				0	[1]	134,706,000,000	[1]		$ 134,700,000,000
Gross Unrealized Gains						1,758,000,000			$ 1,400,000,000
Available-for-sale, written down to fair value				0
Writedown to fair value				0
Available-for-sale, allowance for credit loss				0
OTTI recognized in earnings or other comprehensive income						0		$ 0
Accrued interest receivable				634,000,000
Accrued interest receivable for AFS				0		0
Accrued interest receivable for HTM						471,000,000
Accrued interest writeoff						0
Net unrealized gain (loss) on securities transferred to available for sale from held to maturity [Member]
Schedule of Held-to-maturity Securities [Line Items]
Other comprehensive income (loss), net of tax			$ 19,000,000	1,057,000,000		$ 19,000,000
Trust Deposits [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair value of pledged securities				1,200,000,000
Federal Reserve Bank [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair value of pledged securities				7,900,000,000
FHLB [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair value of pledged securities				$ 44,700,000,000
ASU 2017-12 [Member]
Schedule of Held-to-maturity Securities [Line Items]
Fair value of securities transferred from held to maturity		$ 8,800,000,000

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.