Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Details) - USD ($) $ in Millions		Mar. 31, 2022	Dec. 31, 2021
ASSETS
Trading account assets		$ 848	$ 701
Derivative assets		2,739	1,962
Securities available for sale		43,681	45,364
Held to maturity securities		6,871	7,539
Loans, net of unearned income		106,600	101,854
Loans held for sale	[1]	1,170	2,729
LIABILITIES
Long-term debt		10,814	12,042
Carrying Amount
ASSETS
Trading account assets		848	701
Other investments		722	639
Loans, net of unearned income (residential)		11	11
Loans held for sale		114	281
Securities available for sale		43,681	45,364
Held to maturity securities		6,871	7,539
Loans, net of unearned income		105,484	100,782
Loans held for sale		1,056	2,448
Short-term investments			0
Cash and short-term investments		4,565	11,923
LIABILITIES
Time deposits		3,570	3,858
Short-term borrowings		2,821	761
Long-term debt		10,814	12,042
Deposits with no stated maturity		145,093	148,714
Fair Value
ASSETS
Trading account assets		848	701
Other investments		722	639
Loans, net of unearned income (residential)		11	11
Loans held for sale		114	281
Securities available for sale		43,681	45,364
Held to maturity securities		6,687	7,665
Loans, net of unearned income		104,242	100,428
Loans held for sale		1,056	2,448
Short-term investments			0
Cash and short-term investments		4,565	11,923
LIABILITIES
Time deposits		3,576	3,866
Short-term borrowings		2,821	761
Long-term debt		10,831	12,518
Deposits with no stated maturity		145,093	148,714
Level 1 | Fair Value
ASSETS
Trading account assets		0	0
Other investments		6	24
Loans, net of unearned income (residential)		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		0	0
Short-term investments			0
Cash and short-term investments		4,565	11,923
LIABILITIES
Time deposits		0	0
Short-term borrowings		69	75
Long-term debt		10,146	11,813
Deposits with no stated maturity		0	0
Level 2 | Fair Value
ASSETS
Trading account assets		848	701
Other investments		0	0
Loans, net of unearned income (residential)		0	0
Loans held for sale		114	281
Securities available for sale		43,681	45,364
Held to maturity securities		6,687	7,665
Loans, net of unearned income		0	0
Loans held for sale		0	0
Short-term investments			0
Cash and short-term investments		0	0
LIABILITIES
Time deposits		3,576	3,866
Short-term borrowings		2,752	686
Long-term debt		685	705
Deposits with no stated maturity		145,093	148,714
Level 3 | Fair Value
ASSETS
Trading account assets		0	0
Other investments		639	543
Loans, net of unearned income (residential)		11	11
Loans held for sale		0	0
Securities available for sale		0	0
Held to maturity securities		0	0
Loans, net of unearned income		104,242	100,428
Loans held for sale		1,056	2,448
Short-term investments			0
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
Measured at NAV | Fair Value
ASSETS
Other investments		77	72
Derivatives Not Designated as Hedging Instruments | Carrying Amount
ASSETS
Derivative assets		2,640	1,887
LIABILITIES
Derivative liabilities		609	157
Derivatives Not Designated as Hedging Instruments | Fair Value
ASSETS
Derivative assets		2,640	1,887
Derivative assets, Netting Adjustment		(433)	(320)
LIABILITIES
Derivative liabilities		609	157
Derivative liabilities, Netting Adjustment		(2,727)	(1,526)
Derivatives Not Designated as Hedging Instruments | Level 1 | Fair Value
ASSETS
Derivative assets		92	71
LIABILITIES
Derivative liabilities		85	66
Derivatives Not Designated as Hedging Instruments | Level 2 | Fair Value
ASSETS
Derivative assets		2,937	2,096
LIABILITIES
Derivative liabilities		3,242	1,610
Derivatives Not Designated as Hedging Instruments | Level 3 | Fair Value
ASSETS
Derivative assets		44	40
LIABILITIES
Derivative liabilities		9	7
Derivatives Designated as Hedging Instruments | Carrying Amount
ASSETS
Derivative assets		99	75
LIABILITIES
Derivative liabilities		(11)	4
Derivatives Designated as Hedging Instruments | Fair Value
ASSETS
Derivative assets		99	75
Derivative assets, Netting Adjustment		103	36
LIABILITIES
Derivative liabilities		(11)	4
Derivative liabilities, Netting Adjustment		38	0
Derivatives Designated as Hedging Instruments | Level 1 | Fair Value
ASSETS
Derivative assets		0	0
LIABILITIES
Derivative liabilities		0	0
Derivatives Designated as Hedging Instruments | Level 2 | Fair Value
ASSETS
Derivative assets		(4)	39
LIABILITIES
Derivative liabilities		(49)	4
Derivatives Designated as Hedging Instruments | Level 3 | Fair Value
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 $114 million at March 31, 2022, and $281 million at December 31, 2021.