Guarantor Financial Statement Information - Narrative (Details) $ in Millions	Dec. 31, 2018 USD ($) subsidiary
Unsecured senior notes, net	$ 2,459
Ownership percentage	100.00%
Number of direct wholly owned subsidiaries \| subsidiary	3
Unsecured Senior Notes
Unsecured senior notes principal amount	$ 2,498
Unsecured senior notes, net	$ 2,459
$600 face value, 6.500% interest rate payable semi-annually, due July 2021 \| Unsecured Senior Notes
Interest rate	6.50%
Unsecured senior notes principal amount	$ 592
$300 face value, 6.500% interest rate payable semi-annually, due June 2022 \| Unsecured Senior Notes
Interest rate	6.50%
Unsecured senior notes principal amount	$ 206

Including the current and noncurrent portions, carrying value as of the balance sheet date of uncollateralized debt obligations (with maturities initially due after one year or beyond the operating cycle if longer).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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