Revenue Recognition Revenue Recognition - Contract Liability Balances (Details) - USD ($) $ in Millions	Jun. 30, 2018		Dec. 31, 2017
Contract with Customer, Liability	$ 152	[1]	$ 131	[2]
Contract with Customer, Liability, Noncurrent	6		2
Customer Loyalty Program [Member]
Contract with Customer, Liability	68	[1]	62	[2]
Customer Advances [Member]
Contract with Customer, Liability	$ 84	[1]	$ 69	[2]

[1] (2) $6 million included within Deferred credits and other liabilities.

[2] (1) $2 million included within Deferred credits and other liabilities.