Liability for Policy and Contract Claims - Additional Information (Detail) - Long-term Care Insurance - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred related to insured events of prior year			$ (183)	$ 377	$ 39
Increase (Decrease) in claim reserves		$ 1,285
Changes in Assumptions and Methodologies
Liability for Claims and Claims Adjustment Expense [Line Items]
Incurred related to insured events of prior year				305
Increase (Decrease) in claim reserves		460
Increase in reinsurance recoverable		$ 25		$ 221
Claim Reserve Refinement
Liability for Claims and Claims Adjustment Expense [Line Items]
Increase (Decrease) in claim reserves	$ 222
Increase in reinsurance recoverable	$ 222
Net favorable corrections and adjustments
Liability for Claims and Claims Adjustment Expense [Line Items]
Increase/decrease in reserves					$ (25)