Shareholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Thousands	1 Months Ended	12 Months Ended
	May 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	May 01, 2020
Class of Stock [Line Items]
Proceeds from issuance of equity securities		$ 2,917,000,000	$ 0	$ 0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax		$ 25,000,000
Minimum
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion		5,200
Maximum
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion		6,200
Common Stock  Issued at Par Value
Class of Stock [Line Items]
Convertible Preferred Stock, Shares Issued upon Conversion					11,703
Stock Issued During Period, Shares, New Issues	6,250
Gross Proceeds from Issuance of Equity	$ 1,500,000,000
Convertible Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Depositary Share Ownership Interest, Percentage	5.00%
Preferred Stock, Shares Outstanding					2,475
Stock Issued During Period, Shares, New Issues	1,500
Gross Proceeds from Issuance of Equity	$ 1,500,000,000
Proceeds from Issuance of Preferred Stock and Preference Stock	$ 1,459,000,000
Depositary Share Liquidation		$ 50
Preferred Stock, Liquidation Preference Per Share		$ 1,000
Preferred Stock, Dividend Rate, Percentage		6.00%