Mortgage Loans - Credit Quality Indicators - SF (Details) - Single-family - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	$ 213,309	$ 279,314
One fiscal year before	279,143	489,031
Two fiscal years before	460,802	1,103,809
Three fiscal years before	1,041,742	890,887
Four fiscal years before	838,150	155,447
Prior	839,077	763,925
Total mortgage loans	3,672,223	3,682,413
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	2
One fiscal year, writeoff	30	36
Two fiscal years, writeoff	96	54
Three fiscal years, writeoff	85	46
Four fiscal years, writeoff	46	109
Prior	187	619
Total writeoff	444	866
Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	126,341	157,317
One fiscal year before	179,322	354,060
Two fiscal years before	369,211	1,060,673
Three fiscal years before	1,022,341	887,045
Four fiscal years before	835,796	154,553
Prior	837,222	762,320
Total mortgage loans	3,370,233	3,375,968
Greater than 80% and less than or equal to 90%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	37,476	58,766
One fiscal year before	72,201	97,186
Two fiscal years before	75,293	38,932
Three fiscal years before	17,685	3,432
Four fiscal years before	2,126	806
Prior	1,458	1,167
Total mortgage loans	206,239	200,289
Greater than 90% and less than or equal to 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	49,472	62,216
One fiscal year before	27,272	35,990
Two fiscal years before	15,154	4,014
Three fiscal years before	1,579	363
Four fiscal years before	188	71
Prior	229	230
Total mortgage loans	93,894	102,884
Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	20	1,015
One fiscal year before	348	1,795
Two fiscal years before	1,144	190
Three fiscal years before	137	47
Four fiscal years before	40	17
Prior	168	208
Total mortgage loans	1,857	3,272
20- and 30-year or more, amortizing fixed-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	205,959	268,985
One fiscal year before	269,317	447,259
Two fiscal years before	422,880	932,415
Three fiscal years before	885,929	771,430
Four fiscal years before	730,724	137,546
Prior	730,672	650,407
Total mortgage loans	3,245,481	3,208,042
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	2
One fiscal year, writeoff	29	35
Two fiscal years, writeoff	94	53
Three fiscal years, writeoff	83	45
Four fiscal years, writeoff	45	108
Prior	169	560
Total writeoff	420	803
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	120,077	148,641
One fiscal year before	170,564	314,384
Two fiscal years before	332,411	889,434
Three fiscal years before	866,580	767,596
Four fiscal years before	728,375	136,654
Prior	728,941	648,964
Total mortgage loans	2,946,948	2,905,673
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	36,801	57,686
One fiscal year before	71,312	95,509
Two fiscal years before	74,354	38,790
Three fiscal years before	17,637	3,424
Four fiscal years before	2,121	804
Prior	1,394	1,082
Total mortgage loans	203,619	197,295
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	49,061	61,658
One fiscal year before	27,096	35,602
Two fiscal years before	14,991	4,002
Three fiscal years before	1,575	363
Four fiscal years before	188	71
Prior	196	189
Total mortgage loans	93,107	101,885
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	20	1,000
One fiscal year before	345	1,764
Two fiscal years before	1,124	189
Three fiscal years before	137	47
Four fiscal years before	40	17
Prior	141	172
Total mortgage loans	1,807	3,189
15-year or less, amortizing fixed-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	5,414	7,951
One fiscal year before	7,274	35,931
Two fiscal years before	32,484	165,347
Three fiscal years before	150,228	117,797
Four fiscal years before	105,901	17,162
Prior	81,921	84,225
Total mortgage loans	383,222	428,413
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Current fiscal year, writeoff	0	0
One fiscal year, writeoff	1	0
Two fiscal years, writeoff	2	1
Three fiscal years, writeoff	2	1
Four fiscal years, writeoff	1	1
Prior	2	5
Total writeoff	8	8
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	4,872	7,110
One fiscal year before	6,874	35,224
Two fiscal years before	32,279	165,294
Three fiscal years before	150,217	117,795
Four fiscal years before	105,901	17,162
Prior	81,919	84,222
Total mortgage loans	382,062	426,807
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	320	581
One fiscal year before	369	647
Two fiscal years before	186	52
Three fiscal years before	11	2
Four fiscal years before	0	0
Prior	1	1
Total mortgage loans	887	1,283
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	222	259
One fiscal year before	31	58
Two fiscal years before	19	1
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	0	1
Total mortgage loans	272	319
15-year or less, amortizing fixed-rate | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	1
One fiscal year before	0	2
Two fiscal years before	0	0
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	1	1
Total mortgage loans	1	4
Adjustable-rate
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	1,936	2,378
One fiscal year before	2,552	5,841
Two fiscal years before	5,438	6,047
Three fiscal years before	5,585	1,660
Four fiscal years before	1,525	712
Prior	8,696	9,720
Total mortgage loans	25,732	26,358
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	0	0
Three fiscal years, writeoff	0	0
Four fiscal years, writeoff	0	0
Prior	1	2
Total writeoff	1	3
Adjustable-rate | Less than or equal to 80%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	1,392	1,566
One fiscal year before	1,884	4,452
Two fiscal years before	4,521	5,945
Three fiscal years before	5,544	1,654
Four fiscal years before	1,520	710
Prior	8,693	9,716
Total mortgage loans	23,554	24,043
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	355	499
One fiscal year before	520	1,030
Two fiscal years before	753	90
Three fiscal years before	37	6
Four fiscal years before	5	2
Prior	2	3
Total mortgage loans	1,672	1,630
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	189	299
One fiscal year before	145	330
Two fiscal years before	144	11
Three fiscal years before	4	0
Four fiscal years before	0	0
Prior	1	1
Total mortgage loans	483	641
Adjustable-rate | Greater than 100%
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Current fiscal year	0	14
One fiscal year before	3	29
Two fiscal years before	20	1
Three fiscal years before	0	0
Four fiscal years before	0	0
Prior	0	0
Total mortgage loans	23	44
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	27
Prior	17,788	19,573
Total mortgage loans	17,788	19,600
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	15	52
Total writeoff	15	52
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	27
Prior	17,669	19,418
Total mortgage loans	17,669	19,445
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	61	81
Total mortgage loans	61	81
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	32	39
Total mortgage loans	32	39
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	26	35
Total mortgage loans	26	35
U.S Government
Financing Receivable, before Allowance for Credit Loss, by Origination Year [Abstract]
Total mortgage loans	3,900	5,500
Financing Receivable, Allowance for Credit Loss, Writeoff, by Origination Year [Abstract]
Total writeoff	$ 43	$ 7