Credit Quality and the Allowance for Loan and Lease Losses - Summary of Transactions in the ALLL by Portfolio Segment (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2024		Sep. 30, 2023	Sep. 30, 2024		Sep. 30, 2023	Dec. 31, 2023		Dec. 31, 2022
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	$ 2,288		$ 2,327	$ 2,322	[1]	$ 2,194	$ 2,194
Losses charged off	(183)		(158)	(511)		(389)
Recoveries of losses previously charged off	41		34	115		97
Provision for loan and lease losses	159		137	379		487
Balance, end of period	2,305	[1]	2,340	2,305	[1]	2,340	$ 2,322	[1]	$ 2,194
Accounting Standards Update [Extensible Enumeration]							Accounting Standards Update 2023-02 [Member]		Accounting Standards Update 2022-02 [Member]
Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						(49)	$ (49)
Balance, end of period									$ (49)
Other Consumer Loans, Point of Sale
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Losses charged off	(6)		(8)	(22)		(26)
Recoveries of losses previously charged off	6		8	22		26
Commercial
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	1,113		1,199	1,130		1,127	1,127
Losses charged off	(80)		(70)	(203)		(140)
Recoveries of losses previously charged off	8		6	16		13
Provision for loan and lease losses	64		52	162		183
Balance, end of period	1,105		1,187	1,105		1,187	1,130		1,127
Commercial | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						4	4
Balance, end of period									4
Residential Mortgage
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	136		173	145		245	245
Losses charged off	0		(1)	(2)		(3)
Recoveries of losses previously charged off	1		1	3		3
Provision for loan and lease losses	6		(18)	(3)		(54)
Balance, end of period	143		155	143		155	145		245
Residential Mortgage | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						(36)	(36)
Balance, end of period									(36)
Consumer
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period	1,039		955	1,047		822	822
Losses charged off	(103)		(87)	(306)		(246)
Recoveries of losses previously charged off	32		27	96		81
Provision for loan and lease losses	89		103	220		358
Balance, end of period	$ 1,057		$ 998	$ 1,057		998	1,047		822
Consumer | Cumulative Effect, Period of Adoption, Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Balance, beginning of period						$ (17)	$ (17)
Balance, end of period									$ (17)

[1] Includes $50 and $55 of other short-term investments, $1,131 and $1,573 of portfolio loans and leases, $(21) and $(28) of ALLL, $8 and $10 of other assets, $13 and $14 of other liabilities and $1,008 and $1,409 of long-term debt from consolidated VIEs that are included in their respective captions above at September 30, 2024 and December 31, 2023, respectively. For further information, refer to Note 12.