Leases - Components of Net Investment in Sales-Type and Direct Financing Leases (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Capital Leases, Net Investment in Direct Financing and Sales Type Leases [Abstract]
Accumulated allowance for uncollectible minimum lease payments	$ 94	$ 83

The estimate of contractual payments on direct financing leases that are probable of not being collected as of the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=84165051&loc=d3e45377-112738

Name:	us-gaap_CapitalLeasesNetInvestmentInDirectFinancingLeasesAllowanceForUncollectibleMinimumLeasePayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant