Debt - Revolving Credit Facility (Details)	Jun. 30, 2015	May. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity		$ 3,000,000,000	$ 2,500,000,000.0
Line of Credit Facility, increase in borrowing capacity		500,000,000
Line of credit, extended borrowing capacity		500,000,000
Ratio of indebtedness to net capital	0.29
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity		500,000,000
Bridge Loan [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, maximum borrowing capacity		$ 100,000,000
Maximum [Member]
Line of Credit Facility [Line Items]
Ratio of indebtedness to net capital		0.65