Debt (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2016 USD ($) outstanding_contract contract payment	Dec. 31, 2012 USD ($)	Dec. 31, 2015 USD ($) outstanding_contract
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,500,000,000.0
Line of credit facility, additional borrowing capacity (up to)	$ 500,000,000.0
Debt Instrument, interest, additional interest above eurodollar rate	1.00%
Number of derivative contracts | outstanding_contract	24		105
Notional amount of interest rate derivatives	$ 716,500,000		$ 893,610,000
Letters of credit outstanding, amount	$ 4,000,000
Interest rate swap
Debt Instrument [Line Items]
Number of derivative contracts | contract	3
Notional amount of interest rate derivatives	$ 700,000,000
Derivative, term of contract	30 days
Interest rate, fair value hedge derivative at fair value, net (negative fair value)	$ 17,000,000
Minimum | Interest rate swap
Debt Instrument [Line Items]
Derivative, fixed interest rate	1.53%
Maximum | Interest rate swap
Debt Instrument [Line Items]
Derivative, fixed interest rate	1.60%
Euro Dollar rate
Debt Instrument [Line Items]
Minimum applicable margin rate	1.125%
Maximum applicable margin rate	1.50%
Federal Funds rate
Debt Instrument [Line Items]
Debt instrument, interest, additional interest above federal fund rate	0.50%
Federal Funds rate | Euro Dollar rate
Debt Instrument [Line Items]
Minimum applicable margin rate	0.125%
Maximum applicable margin rate	0.50%
Term loans
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 400,000,000
Debt instruments, maturity duration	5 years
Line of credit facility, frequency of payments | payment	16
Revolver loans
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 1,100,000,000.0
Revolver loans | Letter of credit
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity	$ 40,000,000.0
Connecticut Economic Development Program
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		$ 5,000,000.0
Debt instrument, period principal payments are deferred		5 years