Income Taxes (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Federal tax rate			21.00%	35.00%
Net income tax expense (benefit), tax reform		$ (43)	$ (189)
Net income tax expense (benefit), tax reform, per diluted share		$ (0.07)	$ (0.30)
One-time tax on deemed repatriation of accumulated foreign earnings, offset by unrecognized tax benefits	$ 100
Income taxes	$ 124	$ 109
Effective income tax rate	21.00%	22.00%
Favorable discrete items, percentage impact	3.00%