Accounting Policies - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,536	$ 1,546	$ 1,609	$ 1,567	$ 1,589	$ 1,513	$ 1,509	$ 1,453	$ 6,258	$ 6,063	$ 5,661
Corporate
Disaggregation of Revenue [Line Items]
Total revenue									15	0	0
Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									(125)	(110)	(98)
Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									2,883	2,988	2,535
Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,833	1,683	1,661
Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									815	774	925
Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									837	728	638
Subscription
Disaggregation of Revenue [Line Items]
Total revenue									2,682	2,454	2,364
Subscription | Corporate
Disaggregation of Revenue [Line Items]
Total revenue										0	0
Subscription | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Subscription | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Subscription | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,773	1,614	1,543
Subscription | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									750	704	689
Subscription | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									144	136	132
Non-transaction
Disaggregation of Revenue [Line Items]
Total revenue									1,381	1,338	1,259
Non-transaction | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-transaction | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									125	110	98
Non-transaction | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,506	1,448	1,357
Non-transaction | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-transaction | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-transaction | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-subscription / Transaction
Disaggregation of Revenue [Line Items]
Total revenue									1,428	1,599	1,460
Non-subscription / Transaction | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-subscription / Transaction | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Non-subscription / Transaction | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,377	1,540	1,178
Non-subscription / Transaction | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									40	46	99
Non-subscription / Transaction | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									11	13	183
Non-subscription / Transaction | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Asset-linked fees
Disaggregation of Revenue [Line Items]
Total revenue									542	484	400
Asset-linked fees | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Asset-linked fees | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Asset-linked fees | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Asset-linked fees | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									20	23	19
Asset-linked fees | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Asset-linked fees | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									522	461	381
Sales usage-based royalties
Disaggregation of Revenue [Line Items]
Total revenue									225	188	178
Sales usage-based royalties | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Sales usage-based royalties | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Sales usage-based royalties | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Sales usage-based royalties | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Sales usage-based royalties | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									54	57	53
Sales usage-based royalties | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									171	131	125
Transferred at Point in Time
Disaggregation of Revenue [Line Items]
Total revenue									1,428	1,599	1,460
Transferred at Point in Time | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Transferred at Point in Time | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Transferred at Point in Time | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,377	1,540	1,178
Transferred at Point in Time | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									40	46	99
Transferred at Point in Time | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									11	13	183
Transferred at Point in Time | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									0	0	0
Transferred over Time
Disaggregation of Revenue [Line Items]
Total revenue									4,830	4,464	4,201
Transferred over Time | Corporate
Disaggregation of Revenue [Line Items]
Total revenue									15	0	0
Transferred over Time | Intersegment Elimination
Disaggregation of Revenue [Line Items]
Total revenue									(125)	(110)	(98)
Transferred over Time | Ratings | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,506	1,448	1,357
Transferred over Time | Market Intelligence | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									1,793	1,637	1,562
Transferred over Time | Platts | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									804	761	742
Transferred over Time | Indices | Operating Segments
Disaggregation of Revenue [Line Items]
Total revenue									$ 837	$ 728	$ 638