Income Taxes - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax expense	$ 19	$ 94
Effective tax rate	26.40%	111.90%
Tax cuts and jobs act of 2017, income tax expense		$ 68
US federal blended income tax rate			24.50%