Fair Value Measurements - Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2019 USD ($) shares interest_rate_swap_agreements $ / shares	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) interest_rate_swap_agreements $ / shares	Jun. 30, 2018 USD ($)	Jun. 30, 2020 USD ($)	Dec. 31, 2018 $ / shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Gross	$ 8,944		$ 8,944
Debt Instrument, Convertible, Terms of Conversion Feature			The CEC Convertible Notes are convertible at the option of holders into a number of shares of CEC common stock that is equal to approximately 0.139 shares of CEC common stock per $1.00 principal amount of CEC Convertible Notes, which is equal to an initial conversion price of $7.19 per share. If all the shares were issued on October 6, 2017, they would have represented approximately 17.9% of the shares of CEC common stock outstanding on a fully diluted basis. The holders of the CEC Convertible Notes can convert them at any time after issuance. CEC can convert the CEC Convertible Notes beginning in October 2020 if the last reported sale price of CEC common stock equals or exceeds 140% of the conversion price for the CEC Convertible Notes in effect on each of at least 20 trading days during any 30 consecutive trading day period. As of June 30, 2019, an immaterial amount of the CEC Convertible Notes were converted into shares of CEC common stock. An aggregate of 156 million shares of CEC common stock are issuable upon conversion of the CEC Convertible Notes, of which 151 million shares are net of amounts held by CEC. As of June 30, 2019, the remaining life of the CEC Convertible Notes is 5.30 years.
Derivative, Gain (Loss) on Derivative, Net	298	$ (25)	$ 460	$ (185)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Other Comprehensive Income (Loss)	40	(12)	61	(17)
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax	$ 1	0	$ 1	0
Convertible Debt [Member] | Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.50%		5.50%			7.00%
Convertible Debt [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Convertible, Number of Equity Instruments | shares	156
Debt Instrument, Convertible, Conversion Price | $ / shares	$ 171.61		$ 171.61			$ 122.38
Convertible Debt [Member] | Measurement Input, Discount Rate [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate During Period			5.00%
Convertible Debt [Member] | Measurement Input, Expected Term [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Term			7 years
Forecast [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax					$ 22
Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of Interest Rate Derivatives Held | interest_rate_swap_agreements	10		10
Derivative, Notional Amount	$ 3,000		$ 3,000
Convertible Debt [Member] | Unsecured Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Gross	1,083		1,083
Debt Instrument, Face Amount	$ 1,100		$ 1,100
Debt Instrument, Interest Rate, Stated Percentage	5.00%		5.00%
Liability [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Option, Changes in Fair Value, Gain (Loss)	$ 9	$ (16)	$ 15	$ (26)
NetOfTrust [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Convertible, Number of Equity Instruments | shares	151
Designated as Hedging Instrument [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, Reclassification Adjustment from AOCI for Derecognition, before Tax	$ 1