Subsequent Events - (Details) - Subsequent Event - USD ($)	Jan. 20, 2017	Jan. 05, 2017
Subsequent Event [Line Items]
Line of credit, capacity available for specific purpose	$ 2,275,000,000.000
Bridge Loan
Subsequent Event [Line Items]
Debt instrument term	11 months 29 days
Line of credit, capacity available for specific purpose	$ 300,000,000.0
CEB
Subsequent Event [Line Items]
Anticipated aggregate purchase price		$ 2,600,000,000
Business combination, liabilities anticipated to be incurred		$ 900,000,000
Secured Debt
Subsequent Event [Line Items]
Debt instrument term	7 years
Line of credit, capacity available for specific purpose	$ 1,375,000,000.000
Unsecured Debt
Subsequent Event [Line Items]
Line of credit, capacity available for specific purpose	$ 600,000,000.0