Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Dec. 31, 2023
Loans by origination year
Total retained loans	$ 1,273,047	$ 1,255,688	$ 1,280,870
Gross charge-offs by origination year
Total gross charge-offs	5,107	3,227
Consumer, excluding credit card
Loans by origination year
Total retained loans	382,795	396,195	397,275
Gross charge-offs by origination year
Total gross charge-offs	661	$ 501
Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	14,784		30,605
Term loans originated in 2023/2022	21,528		15,077
Term loans originated in 2022/2021	12,153		13,063
Term loans originated in 2021/2020	9,966		6,624
Term loans originated in 2020/2019	4,649		1,820
Term loans originated prior to 2020/2019	1,296		528
Revolving loans within the revolving period	3,405		3,006
Revolving loans converted to term loans	171		143
Total retained loans	$ 67,952		$ 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	0.61%		0.91%
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2022	1.20%		1.86%
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2021	2.06%		1.75%
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	1.90%		1.15%
% of 30 plus days past due to total retained loans, Term loans originated in 2020/2019	1.42%		2.36%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2020/2019	2.85%		3.22%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	1.06%		0.73%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	28.65%		28.67%
% of 30 plus days past due to total retained loans	1.44%		1.39%
Gross charge-offs by origination year
Gross charge-offs originated in 2024/2023	$ 80		$ 333
Gross charge-offs originated in 2023/2022	189		297
Gross charge-offs originated in 2022/2021	118		161
Gross charge-offs originated in 2021/2020	67		53
Gross charge-offs originated in 2020/2019	21		35
Gross charge-offs originated prior to 2020/2019	45		64
Gross charge-offs originated within the revolving period	0		0
Gross charge-offs originated converted to term loans	2		4
Total gross charge-offs	522		947
Current | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	14,694		30,328
Term loans originated in 2023/2022	21,269		14,797
Term loans originated in 2022/2021	11,903		12,825
Term loans originated in 2021/2020	9,777		6,538
Term loans originated in 2020/2019	4,583		1,777
Term loans originated prior to 2020/2019	1,259		511
Revolving loans within the revolving period	3,369		2,984
Revolving loans converted to term loans	122		102
Total retained loans	66,976		69,862
30–119 days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	90		276
Term loans originated in 2023/2022	258		279
Term loans originated in 2022/2021	250		231
Term loans originated in 2021/2020	185		78
Term loans originated in 2020/2019	58		43
Term loans originated prior to 2020/2019	36		17
Revolving loans within the revolving period	34		19
Revolving loans converted to term loans	27		24
Total retained loans	938		967
120 or more days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2024/2023	0		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	8		0
Term loans originated prior to 2020/2019	1		0
Revolving loans within the revolving period	2		3
Revolving loans converted to term loans	22		17
Total retained loans	$ 38		$ 37