Leases - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Leased Assets [Line Items]
Rent expense	$ 85	$ 94	$ 83
Operating leases, Future Minimum Lease Payments, 2016	59
Operating leases, Future Minimum Lease Payments, 2017	53
Operating leases, Future Minimum Lease Payments, 2018	51
Operating leases, Future Minimum Lease Payments, 2019	46
Operating leases, Future Minimum Lease Payments, 2020	43
Operating leases, Future Minimum Lease Payments, Thereafter	$ 242
CNA Financial [Member]
Operating Leased Assets [Line Items]
Expected year for relocation of office space under lease agreement	2018
Operating leases, Future Minimum Lease Payments, 2016	$ 9
Operating leases, Future Minimum Lease Payments, 2017	10
Operating leases, Future Minimum Lease Payments, 2018	4
Operating leases, Future Minimum Lease Payments, 2019	0
Operating leases, Future Minimum Lease Payments, 2020	5
Operating leases, Future Minimum Lease Payments, Thereafter	$ 138
Operating leases remaining term of contract after reported periods	17 years