Loans and Allowance for Loan Losses - Reconciliation of Changes in Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	$ 538	$ 474
(Reversal of) provision for loan losses	448	59
Loans charged-off	(73)	(28)
Recoveries of loans previously charged-off	10	11
Allowance for loan losses, end of period	1,152	516
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	354	359
(Reversal of) provision for loan losses	274	32
Recoveries of loans previously charged-off		9
Allowance for loan losses, end of period	679	389
Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	184	110
(Reversal of) provision for loan losses	174	27
Recoveries of loans previously charged-off		2
Allowance for loan losses, end of period	473	122
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period		5
(Reversal of) provision for loan losses		0
Loans charged-off		0
Recoveries of loans previously charged-off		0
Allowance for loan losses, end of period		5
Commercial Loans
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off	(32)	(11)
Recoveries of loans previously charged-off	7
Commercial Loans \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	354
Consumer Loans
Allowance for Loan and Lease Losses [Roll Forward]
Loans charged-off	(41)	$ (17)
Recoveries of loans previously charged-off	3
Consumer Loans \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	184
Unallocated
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	0
Cumulative Effect, Period Of Adoption, Adjustment
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	229
Cumulative Effect, Period Of Adoption, Adjustment \| Commercial Loans \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	76
Cumulative Effect, Period Of Adoption, Adjustment \| Consumer Loans \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	153
Cumulative Effect, Period Of Adoption, Adjusted Balance
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	767
Cumulative Effect, Period Of Adoption, Adjusted Balance \| Commercial Loans \| Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	430
Cumulative Effect, Period Of Adoption, Adjusted Balance \| Consumer Loans \| Consumer
Allowance for Loan and Lease Losses [Roll Forward]
Allowance for loan losses, beginning of period	$ 337

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

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Amount of writeoff of financing receivable, charged against allowance for credit loss.

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- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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