Debt - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) time	Dec. 31, 2016 USD ($)	Aug. 17, 2017 USD ($)	Nov. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Commitment fee percentage	0.125%
Debt issuance costs	$ 27,000,000
Debt	6,100,000,000	$ 6,364,000,000
Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity	3,400,000,000.0
Additional borrowing capacity (up to)	$ 975,000,000
Leverage ratio	3.50
Number of times of leverage ratio (up to) | time	2
Unreserved amount	$ 2,100,000,000
Cash portion of purchase price acquisition of interactive data				$ 4,100,000,000
Minimum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.08%
Maximum
Line of Credit Facility [Line Items]
Commitment fee percentage	0.20%
Maximum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Leverage ratio	4.00
Commercial Paper | Revolving Credit Facility
Line of Credit Facility [Line Items]
Funds reserved for commercial paper program	$ 1,200,000,000	$ 1,600,000,000		1,600,000,000
Funds required to support certain subsidiary clearing house commitments	100,000,000
Repayments of commercial paper	$ 409,000,000
Weighted average interest rate	1.49%	0.74%
Commercial paper weighted average maturity period	18 days	18 days
Commercial Paper | Minimum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Commercial paper maturities	2 days
Commercial paper weighted average maturity period		3 days
Commercial Paper | Maximum | Revolving Credit Facility
Line of Credit Facility [Line Items]
Commercial paper maturities	64 days
Commercial paper weighted average maturity period		68 days
Senior Notes
Line of Credit Facility [Line Items]
Face amount			$ 1,000,000,000.0	2,500,000,000.0
Debt issuance costs	$ 5,000,000
2022 Senior Notes
Line of Credit Facility [Line Items]
Senior notes	495,000,000	$ 0
2022 Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Face amount			$ 500,000,000
Percentage bearing fixed interest, rate			2.35%
Debt issuance costs	8,000,000
2020 Senior Notes
Line of Credit Facility [Line Items]
Senior notes	1,240,000,000	1,242,000,000
2020 Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Face amount				$ 1,250,000,000.00
Percentage bearing fixed interest, rate				2.75%
2025 Senior Notes
Line of Credit Facility [Line Items]
Senior notes	1,240,000,000	1,241,000,000
2025 Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Face amount				$ 1,250,000,000.00
Percentage bearing fixed interest, rate				3.75%
2027 Senior Notes
Line of Credit Facility [Line Items]
Senior notes	495,000,000	$ 0
2027 Senior Notes | Senior Notes
Line of Credit Facility [Line Items]
Face amount			$ 500,000,000
Percentage bearing fixed interest, rate			3.10%
NYSE Notes
Line of Credit Facility [Line Items]
Face amount	$ 850,000,000
Percentage bearing fixed interest, rate	2.00%
Federal Funds Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
LIBOR
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
LIBOR | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.875%
LIBOR | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.00%
Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%