Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ 433	$ (209)	974	$ (621)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(11)	(4)	(24)	0
Other comprehensive income (loss) after tax (expense) benefit	444	(205)	998	(621)
Total stockholder's equity at end of period	12,087	11,415	12,087	11,415
Reclassification from AOCI, tax	2	1	5	0
Tax (expense) benefit on other comprehensive income (loss)	(117)	45	(261)	153
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	21	16	30
Other comprehensive income (loss) before reclassifications	(1)	(1)	3	(11)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(1)	0	(1)	(1)
Other comprehensive income (loss) after tax (expense) benefit	0	(1)	4	(10)
Total stockholder's equity at end of period	20	20	20	20
Reclassification from AOCI, tax	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	(1)	1	(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	587	430	61	859
Other comprehensive income (loss) before reclassifications	434	(156)	955	(570)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(2)	3	(7)	18
Other comprehensive income (loss) after tax (expense) benefit	436	(159)	962	(588)
Total stockholder's equity at end of period	1,023	271	1,023	271
Reclassification from AOCI, tax	0	(1)	1	(5)
Tax (expense) benefit on other comprehensive income (loss)	(114)	46	(255)	155
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(768)	(765)	(775)	(775)
Other comprehensive income (loss) before reclassifications	0	0	(1)	0
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(8)	(7)	(16)	(17)
Other comprehensive income (loss) after tax (expense) benefit	8	7	15	17
Total stockholder's equity at end of period	(760)	(758)	(760)	(758)
Reclassification from AOCI, tax	2	2	4	5
Tax (expense) benefit on other comprehensive income (loss)	(2)	(2)	(4)	(5)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(163)	(86)	(180)	(98)
Other comprehensive income (loss) before reclassifications	0	(52)	17	(40)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0	0	0
Other comprehensive income (loss) after tax (expense) benefit	0	(52)	17	(40)
Total stockholder's equity at end of period	(163)	(138)	(163)	(138)
Reclassification from AOCI, tax	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	(324)	(400)	(878)	16
Total stockholder's equity at end of period	$ 120	$ (605)	$ 120	$ (605)