Fair Value Measurements - Fair Value Disclosures of Financial Instruments (Details) - USD ($) $ in Millions		Jun. 30, 2021	Dec. 31, 2020
ASSETS
Trading account assets		$ 851	$ 735
Derivative assets		2,160	1,798
Securities available for sale		34,638	27,556
Amortized cost		6,175	7,595
Held-to-maturity securities		6,474	8,023
Loans, net of unearned income (residential)		100,730	101,185
Loans held for sale	[1]	1,537	1,583
LIABILITIES
Long-term debt		13,211	13,709
Carrying Amount
ASSETS
Trading account assets		851	735
Other investments		635	621
Loans, net of unearned income (residential)		11	11
Loans held for sale		231	264
Securities available for sale		34,638	27,556
Amortized cost		6,175	7,595
Loans, net of unearned income (residential)		99,499	99,548
Loans held for sale		1,306	1,319
Short-term investments			0
Cash and short-term investments		21,252	17,285
LIABILITIES
Time deposits		4,557	5,743
Short-term borrowings		934	979
Long-term debt		13,211	13,709
Deposits with no stated maturity		141,515	129,539
Fair Value
ASSETS
Trading account assets		851	735
Other investments		635	621
Loans, net of unearned income (residential)		11	11
Loans held for sale		231	264
Securities available for sale		34,638	27,556
Held-to-maturity securities		6,474	8,023
Loans, net of unearned income (residential)		99,283	98,946
Loans held for sale		1,306	1,319
Short-term investments			0
Cash and short-term investments		21,252	17,285
LIABILITIES
Time deposits		4,567	5,765
Short-term borrowings		934	979
Long-term debt		13,895	14,659
Deposits with no stated maturity		141,515	129,539
Level 1 | Fair Value
ASSETS
Trading account assets		0	0
Other investments		11	0
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 (residential)		0	0
Loans held for sale		0	0
Short-term investments			0
Cash and short-term investments		21,252	17,285
LIABILITIES
Time deposits		0	0
Short-term borrowings		211	256
Long-term debt		13,172	13,925
Deposits with no stated maturity		0	0
Level 2 | Fair Value
ASSETS
Trading account assets		851	735
Other investments		0	0
Loans, net of unearned income (residential)		0	0
Loans held for sale		231	264
Securities available for sale		34,616	27,543
Held-to-maturity securities		6,474	8,023
Loans, net of unearned income (residential)		0	0
Loans held for sale		0	0
Short-term investments			0
Cash and short-term investments		0	0
LIABILITIES
Time deposits		4,567	5,765
Short-term borrowings		723	723
Long-term debt		723	734
Deposits with no stated maturity		141,515	129,539
Level 3 | Fair Value
ASSETS
Trading account assets		0	0
Other investments		551	555
Loans, net of unearned income (residential)		11	11
Loans held for sale		0	0
Securities available for sale		22	13
Held-to-maturity securities		0	0
Loans, net of unearned income (residential)		99,283	98,946
Loans held for sale		1,306	1,319
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		73	66
Derivatives Not Designated as Hedging Instruments | Carrying Amount
ASSETS
Derivative assets		2,064	1,676
LIABILITIES
Derivative liabilities		152	154
Derivatives Not Designated as Hedging Instruments | Fair Value
ASSETS
Derivative assets		2,064	1,675
Derivative assets, Netting Adjustment		(298)	(433)
LIABILITIES
Derivative liabilities		152	154
Derivative liabilities, Netting Adjustment		(1,428)	(675)
Derivatives Not Designated as Hedging Instruments | Level 1 | Fair Value
ASSETS
Derivative assets		65	78
LIABILITIES
Derivative liabilities		62	72
Derivatives Not Designated as Hedging Instruments | Level 2 | Fair Value
ASSETS
Derivative assets		2,248	1,939
LIABILITIES
Derivative liabilities		1,511	746
Derivatives Not Designated as Hedging Instruments | Level 3 | Fair Value
ASSETS
Derivative assets		49	91
LIABILITIES
Derivative liabilities		7	11
Derivatives Designated as Hedging Instruments | Carrying Amount
ASSETS
Derivative assets		96	123
LIABILITIES
Derivative liabilities		17	(3)
Derivatives Designated as Hedging Instruments | Fair Value
ASSETS
Derivative assets		96	123
Derivative assets, Netting Adjustment		47	53
LIABILITIES
Derivative liabilities		17	(3)
Derivative liabilities, Netting Adjustment		0	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		49	70
LIABILITIES
Derivative liabilities		17	(3)
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 $231 million at June 30, 2021, and $264 million at December 31, 2020.