Leases - Additional Information (Details) - USD ($) $ in Billions	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Finance Lease, Right-of-Use Asset	$ 46.5	$ 36.1
Finance Lease, Right-of-Use-Asset, Accumulated Amortization	$ 23.0	$ 19.8

Amount of lessee's right to use underlying asset under finance lease.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

Name:	us-gaap_FinanceLeaseRightOfUseAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant