LONG-TERM DEBT AND LEASE OBLIGATIONS - Credit Agreement and Letter of Credit Facility (Details)	9 Months Ended
	Sep. 30, 2016 USD ($)
Credit Agreement
LONG-TERM DEBT AND LEASE OBLIGATIONS
Revolving credit facility, maximum borrowing capacity	$ 1,000,000,000
Line of credit facility, subfacility maximum available capacity	300,000,000
Borrowings outstanding	0
Standby letters of credit outstanding	2,000,000
Amount available for borrowing under revolving credit facility	$ 998,000,000
Credit Agreement | Minimum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Unused commitment fee (as a percent)	0.25%
Credit Agreement | Maximum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Unused commitment fee (as a percent)	0.375%
Credit Agreement | Base rate | Minimum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Margin on variable rate (as a percent)	0.25%
Credit Agreement | Base rate | Maximum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Margin on variable rate (as a percent)	0.75%
Credit Agreement | LIBOR | Minimum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Margin on variable rate (as a percent)	1.25%
Credit Agreement | LIBOR | Maximum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Margin on variable rate (as a percent)	1.75%
Letter of Credit Facility
LONG-TERM DEBT AND LEASE OBLIGATIONS
Revolving credit facility, maximum borrowing capacity	$ 180,000,000
Unused commitment fee (as a percent)	0.25%
Standby letters of credit outstanding	$ 144,000,000
Borrowing capacity after increase subject to certain conditions	$ 200,000,000
Secured debt to EBITDA ratio	3.00
Issuance fee (percentage)	1.50%
Issuance fee, based on face amount (percentage)	0.125%
Letter of Credit Facility | Maximum
LONG-TERM DEBT AND LEASE OBLIGATIONS
Number of business days after notice, for reimbursement of amount drawn.	3 days
Unused commitment fee after step down	0.375%
Letter of Credit Facility | Base rate
LONG-TERM DEBT AND LEASE OBLIGATIONS
Margin on variable rate (as a percent)	0.50%