Debt - Conversion (Details) - Senior notes $ in Millions	3 Months Ended
Jun. 30, 2019 USD ($)
Debt Conversion [Line Items]
Amount of notes exchanged	$ 884
6.625% senior notes due 2020
Debt Conversion [Line Items]
Amount of notes exchanged	229
6.875% senior notes due 2020
Debt Conversion [Line Items]
Amount of notes exchanged	134
6.125% senior notes due 2021
Debt Conversion [Line Items]
Amount of notes exchanged	381
5.375% senior notes due 2021
Debt Conversion [Line Items]
Amount of notes exchanged	$ 140

The value of the financial instrument(s) that the original debt is being converted into in a noncash (or part noncash) transaction. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Name:	us-gaap_DebtConversionConvertedInstrumentAmount1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration