Income Taxes - Summary of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Property and casualty claim and claim adjustment expense reserves	$ 108	$ 74
Unearned premium reserves	108	142
Receivables	13	13
Employee benefits	222	243
Deferred retroactive reinsurance benefit	79	68
Net operating loss carryforwards	251	169
Tax credit carryforwards	101	199
Net unrealized losses	24
Basis differential in investment in subsidiary	8	15
Other	197	211
Total deferred tax assets	1,111	1,134
Valuation allowance	(175)	(169)
Net deferred tax assets	936	965
Deferred tax liabilities:
Deferred acquisition costs	(78)	(77)
Net unrealized gains		(263)
Property, plant and equipment	(840)	(765)
Basis differential in investment in subsidiary	(586)	(364)
Other liabilities	(236)	(220)
Total deferred tax liabilities	(1,740)	(1,689)
Net deferred tax liabilities	$ (804)	$ (724)