Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Loans by origination year
Total retained loans	$ 1,285,370	$ 1,265,941	$ 1,280,870
Gross charge-offs by origination year
Total gross charge-offs	7,674	5,096
Consumer, excluding credit card
Loans by origination year
Total retained loans	377,938	397,054	397,275
Gross charge-offs by origination year
Total gross charge-offs	971	$ 809
Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	20,694		30,605
Term loans originated in 2023/2022	18,136		15,077
Term loans originated in 2022/2021	10,774		13,063
Term loans originated in 2021/2020	8,538		6,624
Term loans originated in 2020/2019	3,765		1,820
Term loans originated prior to 2020/2019	933		528
Revolving loans within the revolving period	3,565		3,006
Revolving loans converted to term loans	195		143
Total retained loans	$ 66,600		$ 70,866
% of 30+ days past due to total retained loans by origination year
% of 30 plus days past due to total retained loans, Term loans originated in 2024/2023	0.73%		0.91%
% of 30 plus days past due to total retained loans, Term loans originated in 2023/2022	1.43%		1.86%
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2021	2.32%		1.75%
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	2.24%		1.15%
% of 30 plus days past due to total retained loans, Term loans originated in 2020/2019	1.65%		2.36%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2020/2019	3.22%		3.22%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	0.95%		0.73%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	32.82%		28.67%
% of 30 plus days past due to total retained loans	1.56%		1.39%
Gross charge-offs by origination year
Gross charge-offs originated in 2024/2023	$ 169		$ 333
Gross charge-offs originated in 2023/2022	268		297
Gross charge-offs originated in 2022/2021	171		161
Gross charge-offs originated in 2021/2020	96		53
Gross charge-offs originated in 2020/2019	30		35
Gross charge-offs originated prior to 2020/2019	64		64
Gross charge-offs originated within the revolving period	0		0
Gross charge-offs originated converted to term loans	4		4
Total gross charge-offs	802		947
Current | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	20,542		30,328
Term loans originated in 2023/2022	17,877		14,797
Term loans originated in 2022/2021	10,524		12,825
Term loans originated in 2021/2020	8,347		6,538
Term loans originated in 2020/2019	3,703		1,777
Term loans originated prior to 2020/2019	903		511
Revolving loans within the revolving period	3,531		2,984
Revolving loans converted to term loans	131		102
Total retained loans	65,558		69,862
30–119 days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	151		276
Term loans originated in 2023/2022	258		279
Term loans originated in 2022/2021	250		231
Term loans originated in 2021/2020	187		78
Term loans originated in 2020/2019	55		43
Term loans originated prior to 2020/2019	29		17
Revolving loans within the revolving period	33		19
Revolving loans converted to term loans	34		24
Total retained loans	997		967
120 or more days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	1		1
Term loans originated in 2023/2022	1		1
Term loans originated in 2022/2021	0		7
Term loans originated in 2021/2020	4		8
Term loans originated in 2020/2019	7		0
Term loans originated prior to 2020/2019	1		0
Revolving loans within the revolving period	1		3
Revolving loans converted to term loans	30		17
Total retained loans	$ 45		$ 37