Acquisitions (Intangible Assets) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	May 31, 2016	Feb. 29, 2016
Customer relationships
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Amortization period of intangible assets for tax purposes	15 years
ISE
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 623	$ 623
ISE | Customer relationships
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 148
Discount rate used		9.10%
Estimated average remaining useful life		13 years
ISE | Exchange registrations
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 467
Discount rate used		8.60%
ISE | Trade name
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 8
Discount rate used		8.60%
Boardvantage
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 111		$ 111
Boardvantage | Customer relationships
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 103
Discount rate used		15.50%
Estimated average remaining useful life		14 years
Boardvantage | Technology
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 6
Discount rate used		15.50%
Estimated average remaining useful life		5 years
Boardvantage | Trade name
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 2
Discount rate used		15.00%
Estimated average remaining useful life		1 year
Marketwired
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 31			$ 31
Marketwired | Customer relationships
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 29
Discount rate used		16.40%
Estimated average remaining useful life		6 years
Marketwired | Trade name
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 2
Discount rate used		15.80%
Estimated average remaining useful life		2 years
Nasdaq CXC
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 76			$ 76
Nasdaq CXC | Customer relationships
Finite Lived And Indefinite Lived Intangible Assets [Line Items]
Acquired intangible assets		$ 76
Discount rate used		10.30%
Estimated average remaining useful life		17 years