Basis of Presentation - Adoption of New Accounting Standards (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jan. 01, 2019
New ASU
Lease, Practical Expedients, Package	true
Right-of-use assets	$ 378
Operating lease liability	$ 389
Lease, Practical Expedient, Land Easement [true false]	true
Accounting Standards Update 2016-02 [Member] | Adjustment [Member]
New ASU
Right-of-use assets		$ 385
Operating lease liability		$ 385