Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Details) - USD ($) $ in Millions		Dec. 31, 2021	Dec. 31, 2020
ASSETS
Trading account assets		$ 701	$ 735
Derivative assets		1,962	1,798
Securities available for sale		45,364	27,556
Held-to-maturity securities		7,539	7,595
Loans, net of unearned income		101,854	101,185
Loans held for sale, Carrying Amount	[1]	2,729	1,583
LIABILITIES
Long-term debt, Carrying Amount		12,042	13,709
Carrying Amount
ASSETS
Trading account assets		701	735
Other investments		639	621
Loans, net of allowance		11	11
Loans held for sale		281	264
Securities available for sale		45,364	27,556
Held-to-maturity securities		7,539	7,595
Loans, net of unearned income		100,782	99,548
Loans held for sale, Carrying Amount		2,448	1,319
Cash and short-term investments		11,923	17,285
LIABILITIES
Time deposits, Carrying Amount		3,858	5,743
Short-term borrowings, Carrying Amount		761	979
Long-term debt, Carrying Amount		12,042	13,709
Deposits with no stated maturity		148,714	129,539
Estimate of Fair Value Measurement
ASSETS
Trading account assets		701	735
Other investments		639	621
Loans, net of allowance		11	11
Loans held for sale		281	264
Securities available for sale		45,364	27,556
Held-to-maturity securities		7,665	8,023
Loans, net of unearned income		100,428	98,946
Loans held for sale, Carrying Amount		2,448	1,319
Cash and short-term investments		11,923	17,285
LIABILITIES
Time deposits		3,866	5,765
Short-term borrowings		761	979
Long-term debt		12,518	14,659
Deposits with no stated maturity		148,714	129,539
Estimate of Fair Value Measurement | Level 1
ASSETS
Trading account assets		0	0
Other investments		24	0
Loans, net of allowance		0	0
Loans held for sale		0	0
Securities available for sale		0	0
Held-to-maturity securities		0	0
Loans, net of unearned income		0	0
Loans held for sale, Carrying Amount		0	0
Cash and short-term investments		11,923	17,285
LIABILITIES
Time deposits		0	0
Short-term borrowings		75	256
Long-term debt		11,813	13,925
Deposits with no stated maturity		0	0
Estimate of Fair Value Measurement | Level 2
ASSETS
Trading account assets		701	735
Other investments		0	0
Loans, net of allowance		0	0
Loans held for sale		281	264
Securities available for sale		45,364	27,543
Held-to-maturity securities		7,665	8,023
Loans, net of unearned income		0	0
Loans held for sale, Carrying Amount		0	0
Cash and short-term investments		0	0
LIABILITIES
Time deposits		3,866	5,765
Short-term borrowings		686	723
Long-term debt		705	734
Deposits with no stated maturity		148,714	129,539
Estimate of Fair Value Measurement | Level 3
ASSETS
Trading account assets		0	0
Other investments		543	555
Loans, net of allowance		11	11
Loans held for sale		0	0
Securities available for sale		0	13
Held-to-maturity securities		0	0
Loans, net of unearned income		100,428	98,946
Loans held for sale, Carrying Amount		2,448	1,319
Cash and short-term investments		0	0
LIABILITIES
Time deposits		0	0
Short-term borrowings		0	0
Long-term debt		0	0
Deposits with no stated maturity		0	0
Estimate of Fair Value Measurement | Measured at NAV
ASSETS
Other investments		72	66
Not Designated as Hedging Instrument | Carrying Amount
ASSETS
Derivative assets		1,887	1,676
LIABILITIES
Derivative liabilities		157	154
Not Designated as Hedging Instrument | Estimate of Fair Value Measurement
ASSETS
Derivative assets		1,887	1,675
Derivative assets, netting adjustment		(320)	(433)
LIABILITIES
Derivative liabilities		157	154
Derivative liabilities, netting adjustment		(1,526)	(675)
Not Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 1
ASSETS
Derivative assets		71	78
LIABILITIES
Derivative liabilities		66	72
Not Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 2
ASSETS
Derivative assets		2,096	1,939
LIABILITIES
Derivative liabilities		1,610	746
Not Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 3
ASSETS
Derivative assets		40	91
LIABILITIES
Derivative liabilities		7	11
Designated as Hedging Instrument | Carrying Amount
ASSETS
Derivative assets		75	123
LIABILITIES
Derivative liabilities		4	(3)
Designated as Hedging Instrument | Estimate of Fair Value Measurement
ASSETS
Derivative assets		75	123
Derivative assets, netting adjustment		36	53
LIABILITIES
Derivative liabilities		4	(3)
Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 1
ASSETS
Derivative assets		0	0
LIABILITIES
Derivative liabilities		0	0
Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 2
ASSETS
Derivative assets		39	70
LIABILITIES
Derivative liabilities		4	(3)
Designated as Hedging Instrument | Estimate of Fair Value Measurement | Level 3
ASSETS
Derivative assets		0	0
LIABILITIES
Derivative liabilities		$ 0	$ 0

[1] Total loans held for sale include Real estate — residential mortgage loans held for sale at fair value of $281 million at December 31, 2021, and $264 million at December 31, 2020