DEBT AND OTHER OBLIGATIONS - Letters of Credit (Details) - Letter of Credit	3 Months Ended
	Mar. 31, 2017 USD ($) installment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Jun. 25, 2014 USD ($)	Aug. 07, 2013 USD ($)	Dec. 10, 2010 USD ($)	Apr. 23, 2010 USD ($)
Golden Gate III | Reimbursement Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity under letter of credit							$ 505,000,000
Payments under support agreement obligation	$ 0
Golden Gate III | Second Amended and Restated Reimbursement Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity under letter of credit					$ 710,000,000
Maximum amount up to which LOC will be periodically increased		$ 720,000,000	$ 610,000,000
Golden Gate III | Third Amended and Restated Reimbursement Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity under letter of credit				$ 915,000,000
Maximum amount up to which LOC will be periodically increased		$ 935,000,000	$ 720,000,000
Outstanding letters of credit (LOC)	$ 925,000,000
Letter of credit term	15 years
Future scheduled capital contributions	$ 122,500,000
Number of installments in which future scheduled capital contributions payable | installment	3
Golden Gate IV
Debt Instrument [Line Items]
Maximum borrowing capacity under letter of credit						$ 270,000,000
Maximum amount up to which LOC will be periodically increased	$ 790,000,000
Letter of credit term	12 years
Payments under support agreement obligation	$ 0