Goodwill and Other Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	4 Months Ended	8 Months Ended	12 Months Ended
	Dec. 31, 2017	Aug. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Pre-tax amortization expense, 2018	$ 1,266
Pre-tax amortization expense, 2019	1,254
Pre-tax amortization expense, 2020	1,244
Pre-tax amortization expense, 2021	1,228
Pre-tax amortization expense, 2022	1,221
Successor [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 389
Predecessor [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense		$ 139	$ 319	$ 362