Capital (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 6,726	$ 7,548
Other comprehensive income (loss) before reclassifications, Net unrealized losses	(164)	1
Total other comprehensive income (loss)	(163)	1
Ending Balance	6,733	7,359
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	48	87
Other comprehensive income (loss) before reclassifications, Net unrealized losses	(164)	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0
Total other comprehensive income (loss)	(164)	1
Ending Balance	(116)	88
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4)	(3)
Other comprehensive income (loss) before reclassifications, Net unrealized losses	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	1
Total other comprehensive income (loss)	1	0
Ending Balance	(3)	(3)
Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	44	84
Other comprehensive income (loss) before reclassifications, Net unrealized losses	(164)	1
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	1
Total other comprehensive income (loss)	(163)	1
Ending Balance	$ (119)	$ 85