Closed Block - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Closed Block (Textual) [Abstract]
Policyholder dividend obligation	$ 14	$ 22	$ 26

Closed block operations policy holder dividend obligation excluding adjustment of unrealized gains on available for sale securities.

No definition available.

Name:	nwlic_ClosedBlockOperationsPolicyHolderDividendObligationExcludingAdjustmentOfUnrealizedGainsOnAvailableForSaleSecurities
Namespace Prefix:	nwlic_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration