Stockholders' Equity - Adoption of Accounting Pronouncements (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	$ (5)	$ 66
Retained Earnings [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU	$ (5)	175
Retained Earnings [Member] | Accounting Standards Update 2017-05 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU		66
Retained Earnings [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU		109
Accumulated other comprehensive loss
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU		(109)
Accumulated other comprehensive loss | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of adoption of ASU		$ (109)