Insurance Reserves - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance Reserves [Line Items]
Deferred Policy acquistion costs amortization					$ 342	$ 481	$ 448
Future policy benefit reserves	$ 38,472	$ 37,063			38,472	37,063
Immediate Fixed Annuity | Loss Recognition Testing
Insurance Reserves [Line Items]
Deferred Policy acquistion costs amortization			$ 14
Increase in future policy benefit reserves					89	24
Long-term Care Insurance | Profits Followed By Losses
Insurance Reserves [Line Items]
Future policy benefit reserves	102	30			102	30
Long-term care insurance future policy benefit reserves present value of expected losses	2,800	2,200			2,800	2,200
Federal Home Loan Bank
Insurance Reserves [Line Items]
Federal Home Loan Bank common stock held	37	36			37	36
Amount of funding agreements issued to the Federal Home Loan Bank	280	254			280	254
Letters of credit related to the Federal Home Loan Bank	28	28			28	28
Pledged assets for Federal Home Loan Bank at fair value	388	356			388	356
Variable Annuity | Nontraditional Long-Duration Contracts
Insurance Reserves [Line Items]
Nontraditional long-duration contracts liability	5,577	5,737			5,577	5,737
Guaranteed Minimum Death Benefit | Nontraditional Long-Duration Contracts | Annuity contracts
Insurance Reserves [Line Items]
Nontraditional long-duration contracts liability	94	90			94	90
Guaranteed Minimum Withdrawal And Guaranteed Annuitization Benefit Contracts
Insurance Reserves [Line Items]
Guaranteed annuitization benefit contracts	645	739			$ 645	$ 739
Unlocking
Insurance Reserves [Line Items]
Deferred Policy acquistion costs amortization		144		$ 109
Increase in liability for policyholder account balances	$ 70	$ 202		$ 175