Subsequent Event (Details) (Subsequent Event [Member], KCG Hotspot [Member], USD $) In Millions, unless otherwise specified	1 Months Ended
	Jan. 31, 2015
Subsequent Event [Line Items]
Cash to be received upon close	$ 365.0
Additional proceeds related to tax benefits	70.0
Sale period	3 years
Percentage share in actual tax benefits for the first three years after closing	70.00%
Percentage share in actual tax benefits thereafter	50.00%
Period to exercise one-time option to terminate the continued tax sharing arrangement	30 days
Payment to be received in exchange of the option to terminate the continued tax sharing arrangement	$ 50.0
Period without entitlement to annual tax benefits	3 years
Trigger Event [Member]
Subsequent Event [Line Items]
Rolling period for the average daily notional FX trading volume	60 days
Average daily notional foreign exchange trading volume, threshold percentage	70.00%
After Trigger Event [Member]
Subsequent Event [Line Items]
Rolling period for the average daily notional FX trading volume	15 days
Average daily notional foreign exchange trading volume, threshold percentage	80.00%