Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 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	(1,190)	$ 541
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(69)	(13)
Other comprehensive income (loss) after tax (expense) benefit	(1,121)	554
Total stockholder's equity at end of period	10,362	11,455
Reclassification from AOCI, tax	19	3
Tax (expense) benefit on other comprehensive income (loss)	281	(144)
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	51	(878)
Total stockholder's equity at end of period	(1,070)	(324)
Net unrealized gains (losses) on investments with an allowance for credit losses(1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	0	16
Other comprehensive income (loss) before reclassifications	(48)	4
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(37)	0
Other comprehensive income (loss) after tax (expense) benefit	(11)	4
Total stockholder's equity at end of period	(11)	20
Reclassification from AOCI, tax	10	0
Tax (expense) benefit on other comprehensive income (loss)	3	(1)
Net unrealized gains (losses) on other investments(1)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	1,025	61
Other comprehensive income (loss) before reclassifications	(1,066)	521
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(22)	(5)
Other comprehensive income (loss) after tax (expense) benefit	(1,044)	526
Total stockholder's equity at end of period	(19)	587
Reclassification from AOCI, tax	6	1
Tax (expense) benefit on other comprehensive income (loss)	281	(141)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(833)	(775)
Other comprehensive income (loss) before reclassifications	1	(1)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(10)	(8)
Other comprehensive income (loss) after tax (expense) benefit	11	7
Total stockholder's equity at end of period	(822)	(768)
Reclassification from AOCI, tax	3	2
Tax (expense) benefit on other comprehensive income (loss)	(3)	(2)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(141)	(180)
Other comprehensive income (loss) before reclassifications	(77)	17
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0
Other comprehensive income (loss) after tax (expense) benefit	(77)	17
Total stockholder's equity at end of period	(218)	(163)
Reclassification from AOCI, tax	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0