Debt Debt - Schedule of Maturities of Long-Term Debt (Details) $ in Millions	Jun. 30, 2018 USD ($) interest_rate_swap_agreements
Other Commitments [Line Items]
Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year	$ 31
Long-term Debt, Maturities, Repayments of Principal in Year Two	64
Long-term Debt, Maturities, Repayments of Principal in Year Three	64
Long-term Debt, Maturities, Repayments of Principal in Year Four	64
Long-term Debt, Maturities, Repayments of Principal in Year Five	64
Long-term Debt, Maturities, Repayments of Principal after Year Five	8,718
Long-term debt, Maturities, Repayments of Principal, Total	9,005
Contractual Obligation, Future Minimum Payments Due, Remainder of Fiscal Year	261	[1]
Contractual Obligation, Due in Second Year	534	[1]
Contractual Obligation, Due in Third Year	544	[1]
Contractual Obligation, Due in Fourth Year	544	[1]
Contractual Obligation, Due in Fifth Year	544	[1]
Contractual Obligation, Due after Fifth Year	9,728	[1]
Contractual Obligation	12,155	[1]
Interest Expense [Member]
Other Commitments [Line Items]
Other Commitments, Future Minimum Payments, Remainder of Fiscal Year	230
Other Commitment, Due in Second Year	470
Other Commitment, Due in Third Year	480
Other Commitment, Due in Fourth Year	480
Other Commitment, Due in Fifth Year	480
Other Commitment, Due after Fifth Year	1,010
Other Commitment	$ 3,150
Designated as Hedging Instrument [Member]
Other Commitments [Line Items]
Number of Interest Rate Derivatives Held | interest_rate_swap_agreements	10

[1] (1) Debt principal payments are estimated amounts based on maturity dates and potential borrowings under our revolving credit facilities. Interest payments are estimated based on the forward-looking LIBOR curve and include the estimated impact of the ten interest rate swap agreements (see Note 6). Actual payments may differ from these estimates.