Loans - Consumer, Excluding Credit Card Loan Portfolio, Auto and Other (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Loans by origination year
Total retained loans	$ 1,369,785	$ 1,285,370	$ 1,299,590
Gross charge-offs by origination year
Total gross charge-offs	8,941	7,674
Consumer, excluding credit card
Loans by origination year
Total retained loans	369,859	377,938	376,334
Gross charge-offs by origination year
Total gross charge-offs	814	$ 971
Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2025/2024	21,139		26,356
Term loans originated in 2024/2023	18,478		16,237
Term loans originated in 2023/2022	11,120		9,460
Term loans originated in 2022/2021	6,030		7,198
Term loans originated in 2021/2020	3,922		2,954
Term loans originated prior to 2021/2020	1,314		647
Revolving loans within the revolving period	3,768		3,757
Revolving loans converted to term loans	252		212
Total retained loans	$ 66,023		$ 66,821
% 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 2025/2024	0.55%		0.72%
% of 30 plus days past due to total retained loans, Term loans originated in 2024/2023	0.93%		1.75%
% of 30 plus days past due to total retained loans, Term loans originated in 2023/2022	1.98%		2.74%
% of 30 plus days past due to total retained loans, Term loans originated in 2022/2021	2.95%		2.50%
% of 30 plus days past due to total retained loans, Term loans originated in 2021/2020	2.75%		1.76%
% of 30 plus days past due to total retained loans, Term loans originated prior to 2021/2020	2.36%		3.55%
% of 30 plus days past due to total retained loans, Revolving loans within the revolving period	0.96%		1.14%
% of 30 plus days past due to total retained loans, Revolving loans converted to term loans	30.95%		30.19%
% of 30 plus days past due to total retained loans	1.42%		1.64%
Gross charge-offs by origination year
Gross charge-offs originated in 2025/2024	$ 153		$ 269
Gross charge-offs originated in 2024/2023	180		348
Gross charge-offs originated in 2023/2022	190		224
Gross charge-offs originated in 2022/2021	123		126
Gross charge-offs originated in 2021/2020	56		37
Gross charge-offs originated prior to 2021/2020	64		82
Gross charge-offs originated within the revolving period	0		1
Gross charge-offs originated converted to term loans	6		6
Total gross charge-offs	772		1,093
Current | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2025/2024	21,022		26,165
Term loans originated in 2024/2023	18,306		15,953
Term loans originated in 2023/2022	10,900		9,201
Term loans originated in 2022/2021	5,852		7,014
Term loans originated in 2021/2020	3,813		2,895
Term loans originated prior to 2021/2020	1,282		624
Revolving loans within the revolving period	3,732		3,714
Revolving loans converted to term loans	174		148
Total retained loans	65,081		65,714
30–119 days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2025/2024	117		190
Term loans originated in 2024/2023	171		283
Term loans originated in 2023/2022	219		259
Term loans originated in 2022/2021	178		179
Term loans originated in 2021/2020	108		53
Term loans originated prior to 2021/2020	30		23
Revolving loans within the revolving period	33		40
Revolving loans converted to term loans	45		34
Total retained loans	901		1,061
120 or more days past due | Consumer, excluding credit card | Auto and other
Loans by origination year
Term loans originated in 2025/2024	0		1
Term loans originated in 2024/2023	1		1
Term loans originated in 2023/2022	1		0
Term loans originated in 2022/2021	0		5
Term loans originated in 2021/2020	1		6
Term loans originated prior to 2021/2020	2		0
Revolving loans within the revolving period	3		3
Revolving loans converted to term loans	33		30
Total retained loans	$ 41		$ 46