Accumulated Other Comprehensive Income (Loss) by Component Schedule of Accumulated Other Comprehensive Income (Loss) by Component (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	$ 12,215	$ 11,217
Other comprehensive income (loss) before reclassifications	714	894
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(38)	(35)
Other comprehensive income (loss) after tax (expense) benefit	752	929
Total stockholder's equity at end of period	12,707	12,215
Reclassification from AOCI, tax	10	10
Tax (expense) benefit on other comprehensive income (loss)	(185)	(240)
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	803	51
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	15	16
Other comprehensive income (loss) before reclassifications		(13)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		(12)
Other comprehensive income (loss) after tax (expense) benefit		(1)
Total stockholder's equity at end of period		15
Reclassification from AOCI, tax		3
Tax (expense) benefit on other comprehensive income (loss)		0
Net unrealized gains (losses) on other investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	1,010	61
Other comprehensive income (loss) before reclassifications		957
Amounts reclassified from accumulated other comprehensive income (loss) net of tax		8
Other comprehensive income (loss) after tax (expense) benefit		949
Total stockholder's equity at end of period		1,010
Reclassification from AOCI, tax		(1)
Tax (expense) benefit on other comprehensive income (loss)		(255)
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
Other comprehensive income (loss) before reclassifications	(43)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(43)
Other comprehensive income (loss) after tax (expense) benefit	0
Total stockholder's equity at end of period	0	0
Reclassification from AOCI, tax	12
Tax (expense) benefit on other comprehensive income (loss)	0
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	1,025
Other comprehensive income (loss) before reclassifications	763
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	43
Other comprehensive income (loss) after tax (expense) benefit	720
Total stockholder's equity at end of period	1,745	1,025
Reclassification from AOCI, tax	(12)
Tax (expense) benefit on other comprehensive income (loss)	(189)
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	(53)	(89)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	(38)	(31)
Other comprehensive income (loss) after tax (expense) benefit	(15)	(58)
Total stockholder's equity at end of period	(848)	(833)
Reclassification from AOCI, tax	10	8
Tax (expense) benefit on other comprehensive income (loss)	4	15
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	47	39
Amounts reclassified from accumulated other comprehensive income (loss) net of tax	0	0
Other comprehensive income (loss) after tax (expense) benefit	47	39
Total stockholder's equity at end of period	(94)	(141)
Reclassification from AOCI, tax	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0