Recently Issued or Adopted Accounting Standards - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings (accumulated deficit)	$ 10,427		$ 10,025
Accumulated other comprehensive income (loss)	$ (630)		$ (649)
Accounting Standards Update 2018-03
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings (accumulated deficit)		$ (10)
Accumulated other comprehensive income (loss)		$ 10