Fair Value Measurements - Additional Details (Details) $ / shares in Units, shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($) shares interest_rate_swap_agreements $ / shares	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt			$ 8,965	$ 8,913
Increase (Decrease) in Derivative Liabilities			$ (697)	$ (64)	$ 0
Description of Interest Rate Derivative Activities			During the years ended December 31, 2018 and 2017, respectively, we entered into six and four interest rate swap agreements to fix the interest rate on $2.0 billion and $1.0 billion of variable rate debt.
Derivative, Notional Amount			$ 3,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Gain (Loss) Included in Other Comprehensive Income (Loss)			$ 16
Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Interest Rate, Stated Percentage			7.00%	4.75%
Debt Instrument, Convertible, Conversion Price | $ / shares			$ 122.38
CEC Convertible Notes, Convertible Number of Shares | shares			156
Convertible Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Instrument, Convertible, Conversion Price | $ / shares			$ 7.19
Convertible Debt [Member] | Unsecured Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt			$ 1,083	$ 1,078
Debt Instrument, Interest Rate, Stated Percentage	[1]		5.00%
Debt Instrument, Face Amount			$ 1,100
Scenario, 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		$ 1
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
Liability [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings			$ 24
Liability [Member] | Estimate of Fair Value Measurement [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Measured on Recurring Basis, Gain (Loss) Included in Earnings				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			$ (10)	$ 0
Measurement Input, Expected Term [Member] | Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Expected Term			7 years
Measurement Input, Discount Rate [Member] | Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate			5.00%
Measurement Input, Price Volatility [Member] | Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Expected Volatility Rate				0.30
Measurement Input, Risk Free Interest Rate [Member] | Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assumptions, Expected Volatility Rate				0.023
NetOfTrust [Member] | Convertible Debt [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
CEC Convertible Notes, Convertible Number of Shares | shares			151

[1] (1) Interest rate is fixed, except where noted.