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, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 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	$ 336	$ 1,229	(258)	$ 39
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	14	5	36	(64)
Other comprehensive income (loss) net of tax (expense) benefit	322	1,224	(294)	103
Total stockholder's equity at end of period	12,668	11,645	12,668	11,645
Reclassification from AOCI, tax	(4)	(1)	(9)	18
Tax (expense) benefit on other comprehensive income (loss)	(78)	(319)	82	(38)
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	187	(1,070)	803	51
Total stockholder's equity at end of period	509	154	509	154
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Reclassification from AOCI, tax				2
Tax (expense) benefit on other comprehensive income (loss)				(36)
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	(11)	0	0
Other comprehensive income (loss) before reclassifications	1	(2)	(2)	(50)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	1	(4)	(2)	(41)
Other comprehensive income (loss) net of tax (expense) benefit	0	2	0	(9)
Total stockholder's equity at end of period	0	(9)	0	(9)
Reclassification from AOCI, tax	0	1	1	11
Tax (expense) benefit on other comprehensive income (loss)	0	(1)	0	2
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	1,118	(19)	1,745	1,025
Other comprehensive income (loss) before reclassifications	323	1,209	(270)	143
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	23	18	57	(4)
Other comprehensive income (loss) net of tax (expense) benefit	300	1,191	(327)	147
Total stockholder's equity at end of period	1,418	1,172	1,418	1,172
Reclassification from AOCI, tax	(7)	(4)	(15)
Tax (expense) benefit on other comprehensive income (loss)	(75)	(317)	87
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(839)	(822)	(848)	(833)
Other comprehensive income (loss) before reclassifications	0	(2)	0	(1)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	(10)	(9)	(19)	(19)
Other comprehensive income (loss) net of tax (expense) benefit	10	7	19	18
Total stockholder's equity at end of period	(829)	(815)	(829)	(815)
Reclassification from AOCI, tax	3	2	5	5
Tax (expense) benefit on other comprehensive income (loss)	(3)	(1)	(5)	(4)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(92)	(218)	(94)	(141)
Other comprehensive income (loss) before reclassifications	12	24	14	(53)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	0	0	0	0
Other comprehensive income (loss) net of tax (expense) benefit	12	24	14	(53)
Total stockholder's equity at end of period	(80)	(194)	(80)	(194)
Reclassification from AOCI, tax	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0	$ 0	$ 0