Debt - Debt Fair Value (Details) - Unsecured Notes - Fair value measurements using significant other observable inputs (Level 2) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
2026 Notes
Debt Instrument [Line Items]
Fair value of notes	$ 893	$ 800
2027 Notes
Debt Instrument [Line Items]
Fair value of notes		376
2047 Notes
Debt Instrument [Line Items]
Fair value of notes	$ 456	$ 360

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

No definition available.

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