Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2016	Sep. 30, 2016	May. 16, 2016	Apr. 11, 2016
Subsequent Event [Line Items]
Preferred Stock, Redemption Price Per Share			$ 25
Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Stock Redeemed or Called During Period, Shares	27,870,560
Subsequent Event [Member] | Series A Preferred Stock [Member]
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share				$ 0.53
Dividends Payable				$ 15
Stock Redeemed or Called During Period, Shares	27,870,560
Preferred Stock, Redemption Price Per Share			$ 25
TradeKing Group, Inc. [Member]
Subsequent Event [Line Items]
Payments to Acquire Businesses, Gross		$ 275
Goodwill, Acquired During Period		$ 250