Nature of Operations and Basis of Presentation - Components of Other (Income) Expense, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other components of net periodic benefit cost	$ (8)	$ (8)	$ (25)	$ (25)
Other income, net	(6)	(9)	(22)	(26)
CARE Ratings Limited
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Investments	43		43		$ 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)	(24)	(26)
Net loss from investments	2	0	2	0
Other income, net	$ (6)	$ (9)	$ (22)	$ (26)