Reinsurance - Life Insurance Ceded Business (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reinsurance for Insurance Companies, by Product Segment [Line Items]
Insurance losses and contract holders' benefits	$ 879	$ 874	$ 2,616	$ 2,581
Life Insurance Segment
Reinsurance for Insurance Companies, by Product Segment [Line Items]
Direct earned premiums	79	72	237	223
Ceded earned premiums	(18)	(16)	(52)	(50)
Earned premiums	61	56	185	173
Direct contract holders' benefits incurred	82	73	228	236
Ceded contract holders' benefits incurred	(16)	(14)	(37)	(52)
Insurance losses and contract holders' benefits	$ 66	$ 59	$ 191	$ 184