Commitments and Contingencies (MF Global) (Details) (MF Global Bankruptcy, USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Jan. 31, 2013	Dec. 31, 2013	Oct. 31, 2011
MF Global Bankruptcy
Loss Contingencies [Line Items]
Initial margin posted			$ 73
Margin received to date		17
Remaining margin claims sold to 3rd party	$ 56