Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	1 Months Ended	3 Months Ended	12 Months Ended
	May 31, 2017	Jun. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Class of Stock [Line Items]
Proceeds from issuance of equity securities	$ 4,800,000,000	$ 4,800,000,000	$ 0	$ 4,827,000,000	$ 0
Common Stock Issued at Par Value
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	14,025
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	2,475
Preferred Stock, Depositary Share Ownership Interest, Percentage	5.00%
Preferred Stock, Dividend Rate, Percentage			6.125%
Preferred Stock, Liquidation Preference Per Share			$ 1,000
Depositary Share Liquidation Preference			$ 50
Minimum
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion			11,700
Maximum
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion			14,000