Fair Value Measurements - Carrying Amounts and Estimated Fair Values for Certain Financial Instruments (Details) - USD ($) $ in Millions		Sep. 30, 2021	Dec. 31, 2020
Financial assets:
Cash and due from banks		$ 3,213	$ 3,147
Other short-term investments	[1]	34,203	33,399
Held-to-maturity securities		8	11
Loans and leases held for sale	[2]	5,203	4,741
Total portfolio loans and leases, net		105,957	106,329
Financial liabilities:
Deposits		165,108	159,081
Federal funds purchased		309	300
Other short-term borrowings		949	1,192
Long-term debt	[1]	11,419	14,973
Commercial
Financial assets:
Total portfolio loans and leases, net		66,720	68,997
Net Carrying Amount
Financial assets:
Cash and due from banks		3,213	3,147
Other short-term investments		34,203	33,399
Other securities		518	524
Held-to-maturity securities		8	11
Loans and leases held for sale		3,671	3,260
Total portfolio loans and leases, net		105,801	106,168
Financial liabilities:
Deposits		165,108	159,081
Federal funds purchased		309	300
Other short-term borrowings		949	1,192
Long-term debt		11,419	14,973
Net Carrying Amount | Commercial
Financial assets:
Total portfolio loans and leases, net		65,553	67,541
Net Carrying Amount | Consumer
Financial assets:
Total portfolio loans and leases, net		40,248	38,627
Total Fair Value
Financial assets:
Cash and due from banks		3,213	3,147
Other short-term investments		34,203	33,399
Other securities		518	524
Held-to-maturity securities		8	11
Loans and leases held for sale		3,679	3,269
Total portfolio loans and leases, net		107,624	108,332
Financial liabilities:
Deposits		165,107	159,094
Federal funds purchased		309	300
Other short-term borrowings		949	1,192
Long-term debt		12,643	16,529
Total Fair Value | Commercial
Financial assets:
Total portfolio loans and leases, net		66,235	67,810
Total Fair Value | Consumer
Financial assets:
Total portfolio loans and leases, net		41,389	40,522
Total Fair Value | Level 1
Financial assets:
Cash and due from banks		3,213	3,147
Other short-term investments		34,203	33,399
Other securities		0	0
Held-to-maturity securities		0	0
Loans and leases held for sale		0	0
Total portfolio loans and leases, net		0	0
Financial liabilities:
Deposits		0	0
Federal funds purchased		309	300
Other short-term borrowings		0	0
Long-term debt		11,818	15,606
Total Fair Value | Level 1 | Commercial
Financial assets:
Total portfolio loans and leases, net		0	0
Total Fair Value | Level 1 | Consumer
Financial assets:
Total portfolio loans and leases, net		0	0
Total Fair Value | Level 2
Financial assets:
Cash and due from banks		0	0
Other short-term investments		0	0
Other securities		518	524
Held-to-maturity securities		0	0
Loans and leases held for sale		0	0
Total portfolio loans and leases, net		0	0
Financial liabilities:
Deposits		165,107	159,094
Federal funds purchased		0	0
Other short-term borrowings		949	1,192
Long-term debt		825	923
Total Fair Value | Level 2 | Commercial
Financial assets:
Total portfolio loans and leases, net		0	0
Total Fair Value | Level 2 | Consumer
Financial assets:
Total portfolio loans and leases, net		0	0
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		8	11
Loans and leases held for sale		3,679	3,269
Total portfolio loans and leases, net		107,624	108,332
Financial liabilities:
Deposits		0	0
Federal funds purchased		0	0
Other short-term borrowings		0	0
Long-term debt		0	0
Total Fair Value | Level 3 | Commercial
Financial assets:
Total portfolio loans and leases, net		66,235	67,810
Total Fair Value | Level 3 | Consumer
Financial assets:
Total portfolio loans and leases, net		$ 41,389	$ 40,522

[1] Includes $27 and $55 of other short-term investments, $383 and $756 of portfolio loans and leases, $(3) and $(7) of ALLL, $2 and $5 of other assets, $1 and $2 of other liabilities, and $325 and $656 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2021 and December 31, 2020, respectively. For further information, refer to Note 12.

[2] Includes $1,532 and $1,481 of residential mortgage loans held for sale measured at fair value at September 30, 2021 and December 31, 2020, respectively.