Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net Income/(Loss)	$ 327	$ 360	$ 376
Other Comprehensive Income/(Loss):
Unrealized gain/(loss) on AFS securities	53	(32)	0
Net change in pension and postretirement benefits	3	(4)	3
Net non-credit-related OTTI gain/(loss) on AFS securities:
Net change in fair value of other-than-temporarily impaired securities	(16)	(38)	195
Net amount of OTTI loss reclassified to/(from) other income/(loss)	(3)	(12)	6
Total net non-credit-related OTTI gain/(loss) on AFS securities	(19)	(50)	201
Net Noncredit Portion Of Other Than Temporary Impairment Losses on HTM Securities [Abstract]
Accretion of non-credit-related OTTI loss	2	3	3
Total net non-credit-related OTTI gain/(loss) on HTM securities	2	3	3
Total other comprehensive income/(loss)	39	(83)	207
Total Comprehensive Income/(Loss)	$ 366	$ 277	$ 583