Capital (Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 7,548	$ 7,021	$ 7,401
OCI, Unrealized Holding Gain (Loss) on Securities	(39)	(31)	132
Total other comprehensive income (loss)	(40)	(30)	132
Ending Balance	6,726	7,548	7,021
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	87	118	(14)
OCI, Unrealized Holding Gain (Loss) on Securities	(39)	(31)	132
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0	0
Total other comprehensive income (loss)	(39)	(31)	132
Ending Balance	48	87	118
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(3)	(4)	(4)
OCI, Unrealized Holding Gain (Loss) on Securities	0	0	0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	(1)	1
Total other comprehensive income (loss)	(1)	1	0
Ending Balance	(4)	(3)	(4)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	84	114	(18)
OCI, Unrealized Holding Gain (Loss) on Securities	(39)	(31)	132
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	(1)	1
Total other comprehensive income (loss)	(40)	(30)	132
Ending Balance	$ 44	$ 84	$ 114