Debt Debt - Term Loan (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Aug. 22, 2019	Aug. 22, 2018	Dec. 31, 2016
Debt Instrument, Term Loan [Line Items]
Debt Instrument, Face Amount	$ 9,775			$ 9,989
Term Loan [Member]
Debt Instrument, Term Loan [Line Items]
Debt Instrument, Term	5 years
Debt Instrument, Face Amount	$ 1,500			$ 1,500
Term Loan [Member] | Scenario, Forecast [Member]
Debt Instrument, Term Loan [Line Items]
Premium to Par Percentage, Prior to 3rd Anniversary			4.25%
Premium to Par Percentage Prior to 4th Anniversary		2.125%
Term Loan [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Term Loan [Line Items]
Debt Instrument, Basis Spread on Variable Rate	7.50%
Debt Instrument, Floor Rate	1.00%
Term Loan [Member] | Alternative Base Rate (ABR) [Member]
Debt Instrument, Term Loan [Line Items]
Debt Instrument, Basis Spread on Variable Rate	6.50%
Debt Instrument, Floor Rate	2.00%