Investments in Securities - Maturity Information (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Total Carrying Amount
Total Carrying Amount, Net	$ 802	$ 827
One Year or Less	4
After One Year Through Five Years	23
After Five Years Through Ten Years	31
After Ten Years	744
Total Fair Value
Total Fair Value	806	837
One Year or Less	4
After One Year Through Five Years	24
After Five Years Through Ten Years	32
After Ten Years	746
Fannie Mae
Total Carrying Amount
Total Carrying Amount, Net	478	492
One Year or Less	0
After One Year Through Five Years	3
After Five Years Through Ten Years	15
After Ten Years	460
Total Fair Value
Total Fair Value	476	495
One Year or Less	0
After One Year Through Five Years	3
After Five Years Through Ten Years	16
After Ten Years	457
Other agency
Total Carrying Amount
Total Carrying Amount, Net	11	12
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	1
After Ten Years	10
Total Fair Value
Total Fair Value	12	12
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	1
After Ten Years	11
Alt-A and subprime private-label securities
Total Carrying Amount
Total Carrying Amount, Net	3	3
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	2
After Ten Years	1
Total Fair Value
Total Fair Value	5	5
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	2
After Ten Years	3
Mortgage revenue bonds
Total Carrying Amount
Total Carrying Amount, Net	139	142
One Year or Less	4
After One Year Through Five Years	20
After Five Years Through Ten Years	10
After Ten Years	105
Total Fair Value
Total Fair Value	141	144
One Year or Less	4
After One Year Through Five Years	21
After Five Years Through Ten Years	10
After Ten Years	106
Other mortgage-related securities
Total Carrying Amount
Total Carrying Amount, Net	171	178
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	3
After Ten Years	168
Total Fair Value
Total Fair Value	172	$ 181
One Year or Less	0
After One Year Through Five Years	0
After Five Years Through Ten Years	3
After Ten Years	$ 169