Earnings Per Share (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended		6 Months Ended
	Dec. 31, 2018	Jan. 31, 2018	Jan. 31, 2015	Mar. 31, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 12, 2018
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Treasury stock acquired (in shares)	44,000,000			5,260,687		39,061,269
Treasury stock acquired	$ 201			$ 21	$ 25	$ 180
Treasury stock acquired, average cost per share (in dollars per share)				$ 3.84		$ 4.63
Depositary Shares
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued (in shares)			34,500,000
Dividend payment		$ 27
Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion (in shares)							74,998,614