CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Accounts receivable, allowance	$ 49	$ 47
PP&E, accumulated depreciation	6,570	6,392
Other intangible assets, accumulated amortization	$ 1,644	$ 1,619
Common stock, share issued (in shares)	1	1
Common stock, share outstanding (in shares)	1	1
Common stock, value outstanding	$ 10,050	$ 10,050
Customer relationships
Customer relationships, accumulated amortization	$ 4,458	$ 4,337