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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net income	$ (84)	$ 336	$ 270	$ 291	$ 223	$ 144	$ 272	$ 260	$ 813	$ 899	$ 859
Adjustments to reconcile net income to net cash flows provided by operating activities:
Net realized investment gains (losses)									52	(93)	(50)
Other, net									67	38	29
Total adjustments									414	355	557
Net cash flows provided by operating activities									1,227	1,254	1,416
Cash Flows from Investing Activities
Change in short term investments									168	(6)	258
Other, net									18	20	2
Net cash flows used by investing activities									(177)	(424)	(846)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(896)	(842)	(813)
Proceeds from the issuance of debt									0	496	498
Repayment of debt									(180)	(391)	(358)
Other, net									(9)	(18)	0
Net cash flows used by financing activities									(1,085)	(755)	(673)
Net change in cash									(45)	84	(116)
Cash, beginning of year				355				271	355	271	387
Cash, end of year	310				355				310	355	271
Parent Company
Cash Flows from Operating Activities
Net income									813	899	859
Adjustments to reconcile net income to net cash flows provided by operating activities:
Equity in net income of subsidiaries									(930)	(1,032)	(978)
Dividends received from subsidiaries									1,026	955	765
Net realized investment gains (losses)									0	42	7
Other, net									16	36	21
Total adjustments									112	1	(185)
Net cash flows provided by operating activities									925	900	674
Cash Flows from Investing Activities
Change in short term investments									130	(146)	(9)
Capital contributions to subsidiaries									(2)	0	0
Other, net									0	0	4
Net cash flows used by investing activities									128	(146)	(5)
Cash Flows from Financing Activities
Dividends paid to common stockholders									(896)	(842)	(813)
Proceeds from the issuance of debt									0	496	498
Repayment of debt									(150)	(391)	(358)
Other, net									(7)	(17)	1
Net cash flows used by financing activities									(1,053)	(754)	(672)
Net change in cash									0	0	(3)
Cash, beginning of year				$ 1				$ 1	1	1	4
Cash, end of year	$ 1				$ 1				$ 1	$ 1	$ 1