Stockholders' Equity - Effect of VE Territory Covered Losses Through Coversion Rate Adjustments (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
UK&I preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of as-converted shares of class A common stock (in shares) | shares	0
Effective price per share (in dollars per share) | $ / shares	$ 209.89
Recovery through conversion rate adjustment | $	$ 9
Europe preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of as-converted shares of class A common stock (in shares) | shares	0
Effective price per share (in dollars per share) | $ / shares	$ 209.89
Recovery through conversion rate adjustment | $	$ 6