DEBT - Debt Extinguishment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Debt Instruments [Line Items]
Gain (Loss) on Extinguishment of Debt	$ (101)	$ (27)	$ 7
Senior Notes [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount	2,598	2,145	454
DebtIssuanceCostsandFairValueAdjustments	(12)	30	26
Extinguishment of Debt, Amount	2,586	2,175	480
Extinguishment Of Debt, Redemption Value	2,686	2,201	470
Gain (Loss) on Extinguishment of Debt	100	26	(10)
Senior Notes [Member] | 6.75% Senior Notes due 2022 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount			404
DebtIssuanceCostsandFairValueAdjustments			22
Extinguishment of Debt, Amount			426
Extinguishment Of Debt, Redemption Value			418
Gain (Loss) on Extinguishment of Debt			(8)
Senior Notes [Member] | 3.55% Senior Notes Due 2022 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount	1,356	12
DebtIssuanceCostsandFairValueAdjustments	(6)	0
Extinguishment of Debt, Amount	1,350	12
Extinguishment Of Debt, Redemption Value	1,391	12
Gain (Loss) on Extinguishment of Debt	41	0
Senior Notes [Member] | 3.875% Senior Notes due March 2023 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount	927
DebtIssuanceCostsandFairValueAdjustments	(4)
Extinguishment of Debt, Amount	923
Extinguishment Of Debt, Redemption Value	964
Gain (Loss) on Extinguishment of Debt	41
Senior Notes [Member] | 6.875% Senior Notes due 2023 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount		728	50
DebtIssuanceCostsandFairValueAdjustments		34	4
Extinguishment of Debt, Amount		762	54
Extinguishment Of Debt, Redemption Value		768	52
Gain (Loss) on Extinguishment of Debt		6	$ (2)
Senior Notes [Member] | 4.00% Senior Notes Due 2021 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount	195	405
DebtIssuanceCostsandFairValueAdjustments	(1)	(2)
Extinguishment of Debt, Amount	194	403
Extinguishment Of Debt, Redemption Value	205	418
Gain (Loss) on Extinguishment of Debt	11	15
Senior Notes [Member] | senior notes 4.55 [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount	120
DebtIssuanceCostsandFairValueAdjustments	(1)
Extinguishment of Debt, Amount	119
Extinguishment Of Debt, Redemption Value	126
Gain (Loss) on Extinguishment of Debt	$ 7
Senior Notes [Member] | Senior Notes Due 2022, 3.1% [Member]
Debt Instruments [Line Items]
Debt Instrument, Face Amount		1,000
DebtIssuanceCostsandFairValueAdjustments		(2)
Extinguishment of Debt, Amount		998
Extinguishment Of Debt, Redemption Value		1,003
Gain (Loss) on Extinguishment of Debt		$ 5