Fair Value Measurements - Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Details) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019
Financial assets:
Cash and due from banks		$ 3,221	$ 3,278
Other short-term investments	[1]	28,243	1,950
Held-to-maturity securities	[2]	16	17
Loans and leases held for sale	[3]	912	1,400
Commercial and industrial loans		55,661	50,542
Commercial mortgage loans		11,233	10,963
Commercial construction loans		5,479	5,090
Commercial leases		3,061	3,363
Residential mortgage loans		16,457	16,724
Home equity		5,681	6,083
Indirect secured consumer loans		12,395	11,538
Credit card		2,211	2,532
Other consumer loans		2,875	2,723
Portfolio loans and leases, net		112,357	108,356
Financial liabilities:
Deposits		156,946	127,062
Federal funds purchased		262	260
Other short-term borrowings		1,285	1,011
Long-term debt	[1]	16,327	14,970
Level 1
Financial assets:
Cash and due from banks		3,221	3,278
Other short-term investments		28,243	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		262	260
Other short-term borrowings		0	0
Long-term debt		16,829	15,244
Level 2
Financial assets:
Cash and due from banks		0	0
Other short-term investments		0	0
Other securities		548	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		156,959	127,059
Federal funds purchased		0	0
Other short-term borrowings		1,285	1,011
Long-term debt		965	700
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		16	17
Loans and leases held for sale		57	136
Commercial and industrial loans		54,431	51,128
Commercial mortgage loans		10,713	10,823
Commercial construction loans		5,538	5,249
Commercial leases		2,796	3,133
Residential mortgage loans		17,551	17,509
Home equity		5,895	6,315
Indirect secured consumer loans		12,168	11,331
Credit card		2,034	2,774
Other consumer loans		2,962	2,866
Unallocated ALLL			0
Portfolio loans and leases, net		114,088	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		3,221	3,278
Other short-term investments		28,243	1,950
Other securities		548	556
Held-to-maturity securities		16	17
Loans and leases held for sale		57	136
Commercial and industrial loans		54,672	49,981
Commercial mortgage loans		10,860	10,876
Commercial construction loans		5,381	5,045
Commercial leases		3,019	3,346
Residential mortgage loans		15,945	16,468
Home equity		5,442	6,046
Indirect secured consumer loans		12,224	11,485
Credit card		1,884	2,364
Other consumer loans		2,745	2,683
Unallocated ALLL			(121)
Portfolio loans and leases, net		112,172	108,173
Financial liabilities:
Deposits		156,946	127,062
Federal funds purchased		262	260
Other short-term borrowings		1,285	1,011
Long-term debt		16,327	14,970
Total Fair Value
Financial assets:
Cash and due from banks		3,221	3,278
Other short-term investments		28,243	1,950
Other securities		548	556
Held-to-maturity securities		16	17
Loans and leases held for sale		57	136
Commercial and industrial loans		54,431	51,128
Commercial mortgage loans		10,713	10,823
Commercial construction loans		5,538	5,249
Commercial leases		2,796	3,133
Residential mortgage loans		17,551	17,509
Home equity		5,895	6,315
Indirect secured consumer loans		12,168	11,331
Credit card		2,034	2,774
Other consumer loans		2,962	2,866
Unallocated ALLL			0
Portfolio loans and leases, net		114,088	111,128
Financial liabilities:
Deposits		156,959	127,059
Federal funds purchased		262	260
Other short-term borrowings		1,285	1,011
Long-term debt		$ 17,794	$ 15,944

[1] Includes $66 and $74 of other short-term investments, $1,032 and $1,354 of portfolio loans and leases, $(14) and $(7) of ALLL, $7 and $8 of other assets, $2 and $2 of other liabilities, and $933 and $1,253 of long-term debt from consolidated VIEs that are included in their respective captions above at June 30, 2020 and December 31, 2019, respectively. For further information refer to Note 13.

[2] Fair value of $16 and $17 at June 30, 2020 and December 31, 2019, respectively.

[3] Includes $840 and $1,264 of residential mortgage loans held for sale measured at fair value and $15 and $0 of commercial loans held for sale measured at fair value at June 30, 2020 and December 31, 2019, respectively.