Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period			$ 11,217
Other comprehensive income (loss) before reclassifications	$ 15	$ (149)	989	$ (770)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(4)	3	(28)	3
Other comprehensive income (loss) after tax (expense) benefit	19	(152)	1,017	(773)
Total stockholder's equity at end of period	12,123	11,510	12,123	11,510
Reclassification from AOCI, tax (expense) benefit	2	(1)	7	(1)
Tax (expense) benefit on other comprehensive income (loss)	(13)	41	(274)	194
Net unrealized gains (losses) on investments with OTTI losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	20	20	16	30
Other comprehensive income (loss) before reclassifications	0	(1)	3	(12)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0	(1)	(1)
Other comprehensive income (loss) after tax (expense) benefit	0	(1)	4	(11)
Total stockholder's equity at end of period	20	19	20	19
Reclassification from AOCI, tax (expense) benefit	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	0	0	(2)	3
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	1,023	271	61	859
Other comprehensive income (loss) before reclassifications	44	(148)	999	(718)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	3	10	(4)	28
Other comprehensive income (loss) after tax (expense) benefit	41	(158)	1,003	(746)
Total stockholder's equity at end of period	1,064	113	1,064	113
Reclassification from AOCI, tax (expense) benefit	0	(2)	1	(7)
Tax (expense) benefit on other comprehensive income (loss)	(11)	42	(266)	197
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(760)	(758)	(775)	(775)
Other comprehensive income (loss) before reclassifications	0	0	(1)	0
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(7)	(7)	(23)	(24)
Other comprehensive income (loss) after tax (expense) benefit	7	7	22	24
Total stockholder's equity at end of period	(753)	(751)	(753)	(751)
Reclassification from AOCI, tax (expense) benefit	2	1	6	6
Tax (expense) benefit on other comprehensive income (loss)	(2)	(1)	(6)	(6)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(163)	(138)	(180)	(98)
Other comprehensive income (loss) before reclassifications	(29)	0	(12)	(40)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0	0	0
Other comprehensive income (loss) after tax (expense) benefit	(29)	0	(12)	(40)
Total stockholder's equity at end of period	(192)	(138)	(192)	(138)
Reclassification from AOCI, tax (expense) benefit	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	0	0	0	0
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	120	(605)	(878)	16
Total stockholder's equity at end of period	$ 139	$ (757)	$ 139	$ (757)