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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period			$ 12,215
Other comprehensive income (loss) before reclassifications	$ 1,229	$ 433	39	$ 974
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	5	(11)	(64)	(24)
Other comprehensive income (loss) after tax (expense) benefit	1,224	444	103	998
Total stockholder's equity at end of period	11,645	12,087	11,645	12,087
Reclassification from AOCI, tax	(1)	2	18	5
Tax (expense) benefit on other comprehensive income (loss)	(319)	(117)	(38)	(261)
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(1,070)	(324)	51	(878)
Total stockholder's equity at end of period	154	120	154	120
Net unrealized gains (losses) on investments with an allowance for credit losses
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(11)	20	0	16
Other comprehensive income (loss) before reclassifications	(2)	(1)	(50)	3
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(4)	(1)	(41)	(1)
Other comprehensive income (loss) after tax (expense) benefit	2	0	(9)	4
Total stockholder's equity at end of period	(9)	20	(9)	20
Reclassification from AOCI, tax	1	0	11	0
Tax (expense) benefit on other comprehensive income (loss)	(1)	(1)	2	(2)
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(19)	587	1,025	61
Other comprehensive income (loss) before reclassifications	1,209	434	143	955
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	18	(2)	(4)	(7)
Other comprehensive income (loss) after tax (expense) benefit	1,191	436	147	962
Total stockholder's equity at end of period	1,172	1,023	1,172	1,023
Reclassification from AOCI, tax	(4)	0	2	1
Tax (expense) benefit on other comprehensive income (loss)	(317)	(114)	(36)	(255)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(822)	(768)	(833)	(775)
Other comprehensive income (loss) before reclassifications	(2)	0	(1)	(1)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(9)	(8)	(19)	(16)
Other comprehensive income (loss) after tax (expense) benefit	7	8	18	15
Total stockholder's equity at end of period	(815)	(760)	(815)	(760)
Reclassification from AOCI, tax	2	2	5	4
Tax (expense) benefit on other comprehensive income (loss)	(1)	(2)	(4)	(4)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(218)	(163)	(141)	(180)
Other comprehensive income (loss) before reclassifications	24	0	(53)	17
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0	0	0
Other comprehensive income (loss) after tax (expense) benefit	24	0	(53)	17
Total stockholder's equity at end of period	(194)	(163)	(194)	(163)
Reclassification from AOCI, tax	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0	$ 0	$ 0