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, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	$ 12,707
Other comprehensive income (loss) before reclassifications	(594)	$ (1,190)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	22	(69)
Other comprehensive income (loss) net of tax (expense) benefit	(616)	(1,121)
Total stockholder's equity at end of period	12,089	10,362
Reclassification from AOCI, tax	(5)	19
Tax (expense) benefit on other comprehensive income (loss)	160	281
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	803	51
Total stockholder's equity at end of period	187	(1,070)
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, tax		6
Tax (expense) benefit on other comprehensive income (loss)		281
Net unrealized gains (losses) on other investments | 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	0	0
Other comprehensive income (loss) before reclassifications	(3)	(48)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	(3)	(37)
Other comprehensive income (loss) net of tax (expense) benefit	0	(11)
Total stockholder's equity at end of period	0	(11)
Reclassification from AOCI, tax	1	10
Tax (expense) benefit on other comprehensive income (loss)	0	3
Net unrealized gains (losses) on other investments | Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	1,745	1,025
Other comprehensive income (loss) before reclassifications	(593)	(1,066)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	34	(22)
Other comprehensive income (loss) net of tax (expense) benefit	(627)	(1,044)
Total stockholder's equity at end of period	1,118	(19)
Reclassification from AOCI, tax	(8)
Tax (expense) benefit on other comprehensive income (loss)	162
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(848)	(833)
Other comprehensive income (loss) before reclassifications	0	1
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	(9)	(10)
Other comprehensive income (loss) net of tax (expense) benefit	9	11
Total stockholder's equity at end of period	(839)	(822)
Reclassification from AOCI, tax	2	3
Tax (expense) benefit on other comprehensive income (loss)	(2)	(3)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(94)	(141)
Other comprehensive income (loss) before reclassifications	2	(77)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	0	0
Other comprehensive income (loss) net of tax (expense) benefit	2	(77)
Total stockholder's equity at end of period	(92)	(218)
Reclassification from AOCI, tax	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0