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, 2015	Mar. 31, 2019	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	$ 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
Common Stock
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Shares issued upon conversion (in shares)					74,998,614