Nature of Operations and Basis of Presentation - Components of Other (Income) Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit cost	$ (8)	$ (8)	$ (17)	$ (17)
Other income, net	(11)	(9)	(16)	(18)
CARE Ratings Limited
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investments	48		48		$ 54
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit cost	(8)	(9)	(16)	(18)
Net gain from investments	(3)	0	0	0
Other income, net	$ (11)	$ (9)	$ (16)	$ (18)