Mortgage Loans - Credit Quality Indicators - SF (Details) - Single-family - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	$ 205,874	$ 288,639
One fiscal year before	288,870	265,785
Two fiscal years before	239,072	450,253
Three fiscal years before	420,437	1,020,997
Four fiscal years before	960,246	820,495
Prior	1,508,569	812,958
Total mortgage loans	3,623,068	3,659,127
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	2
One fiscal year, writeoff	37	44
Two fiscal years, writeoff	67	133
Three fiscal years, writeoff	137	116
Four fiscal years, writeoff	81	72
Prior	261	303
Total writeoff	583	670
Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	120,740	165,115
One fiscal year before	177,020	169,482
Two fiscal years before	163,989	359,669
Three fiscal years before	351,476	1,000,638
Four fiscal years before	944,923	818,130
Prior	1,504,959	811,170
Total mortgage loans	3,263,107	3,324,204
Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	36,257	54,914
One fiscal year before	67,391	67,979
Two fiscal years before	57,068	71,956
Three fiscal years before	53,568	18,388
Four fiscal years before	13,188	2,083
Prior	2,932	1,398
Total mortgage loans	230,404	216,718
Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	48,802	68,344
One fiscal year before	43,364	27,646
Two fiscal years before	16,538	16,982
Three fiscal years before	13,172	1,762
Four fiscal years before	1,785	234
Prior	469	233
Total mortgage loans	124,130	115,201
Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	75	266
One fiscal year before	1,095	678
Two fiscal years before	1,477	1,646
Three fiscal years before	2,221	209
Four fiscal years before	350	48
Prior	209	157
Total mortgage loans	5,427	3,004
20- and 30-year or more, amortizing fixed-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	192,369	278,055
One fiscal year before	278,801	256,538
Two fiscal years before	231,177	413,636
Three fiscal years before	387,635	870,282
Four fiscal years before	824,629	716,979
Prior	1,334,935	711,838
Total mortgage loans	3,249,546	3,247,328
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	2
One fiscal year, writeoff	37	43
Two fiscal years, writeoff	66	130
Three fiscal years, writeoff	134	114
Four fiscal years, writeoff	80	71
Prior	224	261
Total writeoff	541	621
20- and 30-year or more, amortizing fixed-rate | Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	109,424	156,136
One fiscal year before	168,156	161,237
Two fiscal years before	156,793	324,160
Three fiscal years before	319,469	849,984
Four fiscal years before	809,345	714,620
Prior	1,331,420	710,162
Total mortgage loans	2,894,607	2,916,299
20- and 30-year or more, amortizing fixed-rate | Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	34,846	53,904
One fiscal year before	66,461	67,163
Two fiscal years before	56,508	71,059
Three fiscal years before	52,956	18,333
Four fiscal years before	13,157	2,078
Prior	2,879	1,338
Total mortgage loans	226,807	213,875
20- and 30-year or more, amortizing fixed-rate | Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	48,025	67,749
One fiscal year before	43,094	27,468
Two fiscal years before	16,415	16,801
Three fiscal years before	13,019	1,757
Four fiscal years before	1,779	233
Prior	448	205
Total mortgage loans	122,780	114,213
20- and 30-year or more, amortizing fixed-rate | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	74	266
One fiscal year before	1,090	670
Two fiscal years before	1,461	1,616
Three fiscal years before	2,191	208
Four fiscal years before	348	48
Prior	188	133
Total mortgage loans	5,352	2,941
15-year or less, amortizing fixed-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	10,073	8,407
One fiscal year before	7,966	6,793
Two fiscal years before	5,671	31,325
Three fiscal years before	27,933	145,266
Four fiscal years before	130,597	102,032
Prior	150,088	75,904
Total mortgage loans	332,328	369,727
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	0
One fiscal year, writeoff	0	1
Two fiscal years, writeoff	1	2
Three fiscal years, writeoff	2	2
Four fiscal years, writeoff	1	1
Prior	3	4
Total writeoff	7	10
15-year or less, amortizing fixed-rate | Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	8,882	7,508
One fiscal year before	7,375	6,455
Two fiscal years before	5,512	31,140
Three fiscal years before	27,846	145,254
Four fiscal years before	130,592	102,032
Prior	150,088	75,904
Total mortgage loans	330,295	368,293
15-year or less, amortizing fixed-rate | Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	795	576
One fiscal year before	499	314
Two fiscal years before	148	168
Three fiscal years before	75	11
Four fiscal years before	5	0
Prior	0	0
Total mortgage loans	1,522	1,069
15-year or less, amortizing fixed-rate | Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	395	323
One fiscal year before	91	24
Two fiscal years before	11	16
Three fiscal years before	12	1
Four fiscal years before	0	0
Prior	0	0
Total mortgage loans	509	364
15-year or less, amortizing fixed-rate | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	1	0
One fiscal year before	1	0
Two fiscal years before	0	1
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	0	0
Total mortgage loans	2	1
Adjustable-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	3,432	2,177
One fiscal year before	2,103	2,454
Two fiscal years before	2,224	5,292
Three fiscal years before	4,869	5,449
Four fiscal years before	5,020	1,484
Prior	8,254	8,162
Total mortgage loans	25,902	25,018
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	0
One fiscal year, writeoff	0	0
Two fiscal years, writeoff	0	1
Three fiscal years, writeoff	1	0
Four fiscal years, writeoff	0	0
Prior	0	1
Total writeoff	1	2
Adjustable-rate | Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	2,434	1,471
One fiscal year before	1,489	1,790
Two fiscal years before	1,684	4,369
Three fiscal years before	4,161	5,400
Four fiscal years before	4,986	1,478
Prior	8,247	8,159
Total mortgage loans	23,001	22,667
Adjustable-rate | Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	616	434
One fiscal year before	431	502
Two fiscal years before	412	729
Three fiscal years before	537	44
Four fiscal years before	26	5
Prior	6	2
Total mortgage loans	2,028	1,716
Adjustable-rate | Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	382	272
One fiscal year before	179	154
Two fiscal years before	112	165
Three fiscal years before	141	4
Four fiscal years before	6	1
Prior	1	1
Total mortgage loans	821	597
Adjustable-rate | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	4	8
Two fiscal years before	16	29
Three fiscal years before	30	1
Four fiscal years before	2	0
Prior	0	0
Total mortgage loans	52	38
Other
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	0	0
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	15,292	17,054
Total mortgage loans	15,292	17,054
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	0
One fiscal year, writeoff	0	0
Two fiscal years, writeoff	0	0
Three fiscal years, writeoff	0	0
Four fiscal years, writeoff	0	0
Prior	34	37
Total writeoff	34	37
Other | Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	0	0
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	15,204	16,945
Total mortgage loans	15,204	16,945
Other | Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	0	0
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	47	58
Total mortgage loans	47	58
Other | Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	0	0
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	20	27
Total mortgage loans	20	27
Other | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	0
One fiscal year before	0	0
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	21	24
Total mortgage loans	21	24
U.S Government
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Total mortgage loans	3,000	3,600
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Total writeoff	$ 5	$ 47