Schedule II. Condensed Financial Information of Registrant (Parent Company) (Schedule of Condensed Financial Information of Registrant, Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities
Net income	$ 387	$ 213	$ 151	$ (61)	$ 273	$ 107	$ 278	$ 342	$ 690	$ 1,000	$ 813
Adjustments to reconcile net income to net cash flows provided by operating activities:
Net investment losses									54	(29)	52
Other, net									(145)	(225)	(223)
Net cash flows provided by operating activities									1,775	1,140	1,227
Cash Flows from Investing Activities
Change in short term investments									(39)	(535)	168
Other, net									16	15	18
Net cash flows used by investing activities									(705)	(225)	(177)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(950)	(929)	(896)
Proceeds from the issuance of debt									495	496	0
Repayment of debt									(419)	(520)	(180)
Purchase of treasury stock									(18)	(23)	0
Other, net									(10)	(12)	(9)
Net cash flows used by financing activities									(902)	(988)	(1,085)
Cash, beginning of year				242					242
Cash, end of year	419				242				419	242
Parent Company
Cash Flows from Operating Activities
Net income									690	1,000	813
Adjustments to reconcile net income to net cash flows provided by operating activities:
Equity in net income of subsidiaries									(812)	(1,119)	(930)
Dividends received from subsidiaries									975	1,065	1,026
Net investment losses									20	21	0
Other, net									26	13	16
Net cash flows provided by operating activities									899	980	925
Cash Flows from Investing Activities
Change in short term investments									2	10	130
Capital contributions to subsidiaries									(1)	(2)	(2)
Other, net									0	0	0
Net cash flows used by investing activities									1	8	128
Cash Flows from Financing Activities
Dividends paid to common stockholders									(950)	(929)	(896)
Proceeds from the issuance of debt									495	496	0
Repayment of debt									(419)	(520)	(150)
Purchase of treasury stock									(18)	(23)	0
Other, net									(9)	(12)	(7)
Net cash flows used by financing activities									(901)	(988)	(1,053)
Net change in cash									(1)	0	0
Cash, beginning of year				$ 1				$ 1	1	1	1
Cash, end of year	$ 0				$ 1				$ 0	$ 1	$ 1