SCHEDULE I-PARENT COMPANY FINANCIAL INFORMATION (Condensed Statements of Comprehensive Income) (Detail) - 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
Condensed Financial Statements, Captions [Line Items]
Net income	$ 355	$ 644	$ 193	$ 491	$ 184	$ 499	$ 650	$ 1,115	$ 1,683	$ 2,448	$ 614
Other comprehensive income (loss):
Change in gross unrealized investment losses/gains									(189)	149	(101)
Effect of income taxes									51	(55)	38
Total change in unrealized investment gains/losses, net of tax									(138)	94	(63)
Reclassification adjustment for net realized gains included in investment income									(53)	(14)	(96)
Effect of income taxes									17	5	35
Total reclassification adjustment, net of tax									(36)	(9)	(61)
Other comprehensive (loss) income, net of tax									(174)	85	(124)
Comprehensive income attributable to our equity method investment in Kindred at Home									(4)	0	0
Comprehensive income									1,505	2,533	490
Parent Company
Condensed Financial Statements, Captions [Line Items]
Net income									1,683	2,448	614
Other comprehensive income (loss):
Change in gross unrealized investment losses/gains									(189)	149	(101)
Effect of income taxes									51	(55)	38
Total change in unrealized investment gains/losses, net of tax									(138)	94	(63)
Reclassification adjustment for net realized gains included in investment income									(53)	(14)	(96)
Effect of income taxes									17	5	35
Total reclassification adjustment, net of tax									(36)	(9)	(61)
Other comprehensive (loss) income, net of tax									(174)	85	(124)
Comprehensive income attributable to our equity method investment in Kindred at Home									(4)	0	0
Comprehensive income									$ 1,505	$ 2,533	$ 490