Accumulated Other Comprehensive Income (Loss) by Component (Schedule of accumulated other comprehensive income (loss) by component) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 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	$ (155)	$ 268	(413)	$ 307
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	8	11	44	(53)
Other comprehensive income (loss) net of tax (expense) benefit	(163)	257	(457)	360
Total stockholder's equity at end of period	12,664	12,021	12,664	12,021
Reclassification from AOCI, tax	(3)	(4)	(12)	14
Tax (expense) benefit on other comprehensive income (loss)	35	(60)	117	(98)
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	509	154	803	51
Total stockholder's equity at end of period	346	411	346	411
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	(9)	0	0
Other comprehensive income (loss) before reclassifications	0	2	(2)	(48)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	0	(4)	(2)	(45)
Other comprehensive income (loss) net of tax (expense) benefit	0	6	0	(3)
Total stockholder's equity at end of period	0	(3)	0	(3)
Reclassification from AOCI, tax	0	1	1	12
Tax (expense) benefit on other comprehensive income (loss)	0	(1)	0	1
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	1,418	1,172	1,745	1,025
Other comprehensive income (loss) before reclassifications	(121)	231	(391)	374
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	17	24	74	20
Other comprehensive income (loss) net of tax (expense) benefit	(138)	207	(465)	354
Total stockholder's equity at end of period	1,280	1,379	1,280	1,379
Reclassification from AOCI, tax	(5)	(7)	(20)	(5)
Tax (expense) benefit on other comprehensive income (loss)	37	(56)	124	(92)
Pension and postretirement benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(829)	(815)	(848)	(833)
Other comprehensive income (loss) before reclassifications	(1)	(2)	(1)	(3)
Amounts reclassified from accumulated other comprehensive income (loss) net of tax (expense) benefit	(9)	(9)	(28)	(28)
Other comprehensive income (loss) net of tax (expense) benefit	8	7	27	25
Total stockholder's equity at end of period	(821)	(808)	(821)	(808)
Reclassification from AOCI, tax	2	2	7	7
Tax (expense) benefit on other comprehensive income (loss)	(2)	(3)	(7)	(7)
Cumulative foreign currency translation adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total stockholder's equity at beginning of period	(80)	(194)	(94)	(141)
Other comprehensive income (loss) before reclassifications	(33)	37	(19)	(16)
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	(33)	37	(19)	(16)
Total stockholder's equity at end of period	(113)	(157)	(113)	(157)
Reclassification from AOCI, tax	0	0	0	0
Tax (expense) benefit on other comprehensive income (loss)	$ 0	$ 0	$ 0	$ 0