Fair Value Measurements (Carrying Amounts and Estimated Fair Values for Certain Financial Instruments) (Detail) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financial assets:
Cash and due from banks	$ 3,282	$ 3,278	$ 2,749	$ 2,681
Other short-term investments	6,319	1,950
Held-to-maturity securities	17	17
Loans and leases held for sale	1,630	1,400
Commercial and industrial loans	58,250	50,542
Commercial mortgage loans	11,160	10,963
Commercial construction loans	5,462	5,090
Commercial leases	3,123	3,363
Residential mortgage loans	16,701	16,724
Home equity	5,963	6,083
Indirect secured consumer loans	12,050	11,538
Credit card	2,417	2,532
Other consumer loans	2,911	2,723
Portfolio loans and leases, net	115,689	108,356
Financial liabilities:
Deposits	135,061	127,062
Federal funds purchased	1,625	260
Other short-term borrowings	4,542	1,011
Long-term debt	16,282	14,970
Fair Value, Inputs, Level 1
Financial assets:
Cash and due from banks	3,282	3,278
Other short-term investments	6,319	1,950
Other securities	0	0
Held-to-maturity securities	0	0
Loans and leases held for sale	0	0
Commercial and industrial loans	0	0
Commercial mortgage loans	0	0
Commercial construction loans	0	0
Commercial leases	0	0
Residential mortgage loans	0	0
Home equity	0	0
Indirect secured consumer loans	0	0
Credit card	0	0
Other consumer loans	0	0
Unallocated Allowance for Loan and Lease Losses		0
Portfolio loans and leases, net	0	0
Financial liabilities:
Deposits	0	0
Federal funds purchased	1,625	260
Other short-term borrowings	0	0
Long-term debt	15,990	15,244
Fair Value, Inputs, Level 2
Financial assets:
Cash and due from banks	0	0
Other short-term investments	0	0
Other securities	616	556
Held-to-maturity securities	0	0
Loans and leases held for sale	0	0
Commercial and industrial loans	0	0
Commercial mortgage loans	0	0
Commercial construction loans	0	0
Commercial leases	0	0
Residential mortgage loans	0	0
Home equity	0	0
Indirect secured consumer loans	0	0
Credit card	0	0
Other consumer loans	0	0
Unallocated Allowance for Loan and Lease Losses		0
Portfolio loans and leases, net	0	0
Financial liabilities:
Deposits	135,065	127,059
Federal funds purchased	0	0
Other short-term borrowings	4,542	1,011
Long-term debt	885	700
Fair Value, Inputs, Level 3
Financial assets:
Cash and due from banks	0	0
Other short-term investments	0	0
Other securities	0	0
Held-to-maturity securities	17	17
Loans and leases held for sale	57	136
Commercial and industrial loans	56,397	51,128
Commercial mortgage loans	10,767	10,823
Commercial construction loans	5,579	5,249
Commercial leases	2,772	3,133
Residential mortgage loans	17,896	17,509
Home equity	5,934	6,315
Indirect secured consumer loans	11,902	11,331
Credit card	2,339	2,774
Other consumer loans	3,002	2,866
Unallocated Allowance for Loan and Lease Losses		0
Portfolio loans and leases, net	116,588	111,128
Financial liabilities:
Deposits	0	0
Federal funds purchased	0	0
Other short-term borrowings	0	0
Long-term debt	0	0
Net Carrying Amount
Financial assets:
Cash and due from banks	3,282	3,278
Other short-term investments	6,319	1,950
Other securities	616	556
Held-to-maturity securities	17	17
Loans and leases held for sale	57	136
Commercial and industrial loans	57,273	49,981
Commercial mortgage loans	10,923	10,876
Commercial construction loans	5,409	5,045
Commercial leases	3,077	3,346
Residential mortgage loans	16,256	16,468
Home equity	5,745	6,046
Indirect secured consumer loans	11,921	11,485
Credit card	2,111	2,364
Other consumer loans	2,789	2,683
Unallocated Allowance for Loan and Lease Losses		(121)
Portfolio loans and leases, net	115,504	108,173
Financial liabilities:
Deposits	135,061	127,062
Federal funds purchased	1,625	260
Other short-term borrowings	4,542	1,011
Long-term debt	16,282	14,970
Total Fair Value
Financial assets:
Cash and due from banks	3,282	3,278
Other short-term investments	6,319	1,950
Other securities	616	556
Held-to-maturity securities	17	17
Loans and leases held for sale	57	136
Commercial and industrial loans	56,397	51,128
Commercial mortgage loans	10,767	10,823
Commercial construction loans	5,579	5,249
Commercial leases	2,772	3,133
Residential mortgage loans	17,896	17,509
Home equity	5,934	6,315
Indirect secured consumer loans	11,902	11,331
Credit card	2,339	2,774
Other consumer loans	3,002	2,866
Unallocated Allowance for Loan and Lease Losses		0
Portfolio loans and leases, net	116,588	111,128
Financial liabilities:
Deposits	135,065	127,059
Federal funds purchased	1,625	260
Other short-term borrowings	4,542	1,011
Long-term debt	$ 16,875	$ 15,944

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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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