Acquisitions and Divestitures - Divestitures Narrative (Details) $ in Millions	1 Months Ended			3 Months Ended		12 Months Ended
	Jan. 31, 2017 USD ($)	Oct. 31, 2016 USD ($) business	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Apr. 30, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held-for-sale									$ 5
Pre-tax gain (loss) on dispositions				$ 379	$ 722	$ 1,100
Gain (loss) on disposition of business, net of tax				$ 297	$ 521
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions							$ 1,100
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Quant House SAS
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions	$ (31)
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Equity Research
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions		$ 9
Gain (loss) on disposition of business, net of tax		5
Disposal Group, Disposed of by Sale, Not Discontinued Operations | SPSE and CMA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions		364
Gain (loss) on disposition of business, net of tax		$ 297
Number of businesses disposed | business		2
Cash proceeds from sale of business		$ 425
Disposal Group, Disposed of by Sale, Not Discontinued Operations | J.D. Power
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions			$ 728
Gain (loss) on disposition of business, net of tax			516
Cash proceeds from sale of business			$ 1,100
Disposal Group, Disposed of by Sale, Not Discontinued Operations | McGraw Hill Construction
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Pre-tax gain (loss) on dispositions								$ 11