Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Statement of Comprehensive Income [Abstract]
Net Income/(Loss)	$ (8)	$ 104
Other Comprehensive Income/(Loss):
Unrealized gain/(loss) on AFS securities	(502)	38
Net non-credit-related OTTI gain/(loss) on AFS securities
Total net non-credit-related OTTI gain/(loss) on AFS securities	0	14
Net Noncredit Portion Of Other Than Temporary Impairment Losses on HTM Securities [Abstract]
Total other comprehensive income/(loss)	(502)	52
Total Comprehensive Income/(Loss)	$ (510)	$ 156