Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Other assets
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	$ 98	$ 81
Aggregate unpaid principal balance of assets for which fair value option was elected	102	69
Fair value option aggregate difference assets	(4)	12
Other borrowed funds
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value of liabilities for which fair value option was elected	26	32
Aggregate unpaid principal balance, other borrowed funds	26	33
Difference, Other borrowed funds		(1)
Residential mortgage loans held for sale | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	1,504	855
Aggregate unpaid principal balance of assets for which fair value option was elected	1,466	821
Fair value option aggregate difference assets	38	34
Residential mortgage loans held for sale | Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	1,727	1,365
Aggregate unpaid principal balance of assets for which fair value option was elected	2,054	1,645
Fair value option aggregate difference assets	(327)	(280)
Residential mortgage loans held for sale | Accruing loans less than 90 days past due | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	1,451	831
Aggregate unpaid principal balance of assets for which fair value option was elected	1,404	793
Fair value option aggregate difference assets	47	38
Residential mortgage loans held for sale | Accruing loans less than 90 days past due | Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	714	519
Aggregate unpaid principal balance of assets for which fair value option was elected	733	530
Fair value option aggregate difference assets	(19)	(11)
Residential mortgage loans held for sale | Accruing loans 90 days or more past due | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	3	4
Aggregate unpaid principal balance of assets for which fair value option was elected	3	4
Residential mortgage loans held for sale | Accruing loans 90 days or more past due | Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	290	283
Aggregate unpaid principal balance of assets for which fair value option was elected	308	295
Fair value option aggregate difference assets	(18)	(12)
Residential mortgage loans held for sale | Nonaccrual loans | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	50	20
Aggregate unpaid principal balance of assets for which fair value option was elected	59	24
Fair value option aggregate difference assets	(9)	(4)
Residential mortgage loans held for sale | Nonaccrual loans | Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	723	563
Aggregate unpaid principal balance of assets for which fair value option was elected	1,013	820
Fair value option aggregate difference assets	(290)	(257)
Commercial real estate | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	217	362
Aggregate unpaid principal balance of assets for which fair value option was elected	234	376
Fair value option aggregate difference assets	(17)	(14)
Commercial real estate | Accruing loans less than 90 days past due | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	217	357
Aggregate unpaid principal balance of assets for which fair value option was elected	234	370
Fair value option aggregate difference assets	(17)	(13)
Commercial real estate | Nonaccrual loans | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets		5
Aggregate unpaid principal balance of assets for which fair value option was elected		6
Fair value option aggregate difference assets		$ (1)
Other consumer loans held for sale | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	239
Aggregate unpaid principal balance of assets for which fair value option was elected	253
Fair value option aggregate difference assets	(14)
Other consumer loans held for sale | Accruing loans less than 90 days past due | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets	239
Aggregate unpaid principal balance of assets for which fair value option was elected	252
Fair value option aggregate difference assets	(13)
Other consumer loans held for sale | Accruing loans 90 days or more past due | Loans held for sale
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair value - assets
Aggregate unpaid principal balance of assets for which fair value option was elected	1
Fair value option aggregate difference assets	$ (1)