Debt - Annual Estimated Debt Service Requirements (Details) $ in Millions	Dec. 31, 2019 USD ($) interest_rate_swap_agreement
Maturities of Long-term Debt [Abstract]
Total debt	$ 8,665
Designated as Hedging Instrument
Maturities of Long-term Debt [Abstract]
Number of interest rate derivatives held \| interest_rate_swap_agreement	10
Annual maturities of long-term debt
Maturities of Long-term Debt [Abstract]
2020	$ 64
2021	64
2022	64
2023	64
2024	6,666
Thereafter	1,743
Total debt	8,665
Estimated interest payments
Maturities of Long-term Debt [Abstract]
2020	430
2021	410
2022	400
2023	390
2024	380
Thereafter	100
Total debt	2,110
Total debt service obligation
Maturities of Long-term Debt [Abstract]
2020	494
2021	474
2022	464
2023	454
2024	7,046
Thereafter	1,843
Total debt	$ 10,775

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 3
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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Number of interest rate derivative instruments held by the entity at the reporting date.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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