Fair Value Measurements - Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Details) - USD ($) $ in Millions		Sep. 30, 2020	Dec. 31, 2019
Financial assets:
Cash and due from banks		$ 2,996	$ 3,278
Other short-term investments	[1]	31,285	1,950
Held-to-maturity securities	[2]	15	17
Loans and leases held for sale	[3]	2,323	1,400
Commercial and industrial loans		51,695	50,542
Commercial mortgage loans		10,878	10,963
Commercial construction loans		5,656	5,090
Commercial leases		3,021	3,363
Residential mortgage loans		16,158	16,724
Home equity		5,455	6,083
Indirect secured consumer loans		12,925	11,538
Credit card		2,087	2,532
Other consumer loans		2,856	2,723
Portfolio loans and leases, net		108,157	108,356
Financial liabilities:
Deposits		156,683	127,062
Federal funds purchased		251	260
Other short-term borrowings		1,196	1,011
Long-term debt	[1]	15,123	14,970
Net Carrying Amount
Financial assets:
Cash and due from banks		2,996	3,278
Other short-term investments		31,285	1,950
Other securities		531	556
Held-to-maturity securities		15	17
Loans and leases held for sale		851	136
Commercial and industrial loans		50,673	49,981
Commercial mortgage loans		10,505	10,876
Commercial construction loans		5,551	5,045
Commercial leases		2,988	3,346
Residential mortgage loans		15,687	16,468
Home equity		5,244	6,046
Indirect secured consumer loans		12,797	11,485
Credit card		1,802	2,364
Other consumer loans		2,736	2,683
Unallocated ALLL			(121)
Portfolio loans and leases, net		107,983	108,173
Financial liabilities:
Deposits		156,683	127,062
Federal funds purchased		251	260
Other short-term borrowings		1,196	1,011
Long-term debt		15,123	14,970
Total Fair Value
Financial assets:
Cash and due from banks		2,996	3,278
Other short-term investments		31,285	1,950
Other securities		531	556
Held-to-maturity securities		15	17
Loans and leases held for sale		851	136
Commercial and industrial loans		50,465	51,128
Commercial mortgage loans		10,366	10,823
Commercial construction loans		5,711	5,249
Commercial leases		2,868	3,133
Residential mortgage loans		17,240	17,509
Home equity		5,645	6,315
Indirect secured consumer loans		12,704	11,331
Credit card		1,952	2,774
Other consumer loans		2,941	2,866
Unallocated ALLL			0
Portfolio loans and leases, net		109,892	111,128
Financial liabilities:
Deposits		156,697	127,059
Federal funds purchased		251	260
Other short-term borrowings		1,196	1,011
Long-term debt		16,601	15,944
Total Fair Value | Level 1
Financial assets:
Cash and due from banks		2,996	3,278
Other short-term investments		31,285	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 ALLL			0
Portfolio loans and leases, net		0	0
Financial liabilities:
Deposits		0	0
Federal funds purchased		251	260
Other short-term borrowings		0	0
Long-term debt		15,651	15,244
Total Fair Value | Level 2
Financial assets:
Cash and due from banks		0	0
Other short-term investments		0	0
Other securities		531	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 ALLL			0
Portfolio loans and leases, net		0	0
Financial liabilities:
Deposits		156,697	127,059
Federal funds purchased		0	0
Other short-term borrowings		1,196	1,011
Long-term debt		950	700
Total Fair Value | 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		15	17
Loans and leases held for sale		851	136
Commercial and industrial loans		50,465	51,128
Commercial mortgage loans		10,366	10,823
Commercial construction loans		5,711	5,249
Commercial leases		2,868	3,133
Residential mortgage loans		17,240	17,509
Home equity		5,645	6,315
Indirect secured consumer loans		12,704	11,331
Credit card		1,952	2,774
Other consumer loans		2,941	2,866
Unallocated ALLL			0
Portfolio loans and leases, net		109,892	111,128
Financial liabilities:
Deposits		0	0
Federal funds purchased		0	0
Other short-term borrowings		0	0
Long-term debt		$ 0	$ 0

[1] Includes $61 and $74 of other short-term investments, $887 and $1,354 of portfolio loans and leases, $(9) and $(7) of ALLL, $5 and $8 of other assets, $2 and $2 of other liabilities, and $786 and $1,253 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2020 and December 31, 2019, respectively. For further information refer to Note 13.

[2] Fair value of $15 and $17 at September 30, 2020 and December 31, 2019, respectively.

[3] Includes $1,472 and $1,264 of residential mortgage loans held for sale measured at fair value at September 30, 2020 and December 31, 2019, respectively.