Stockholders' Equity Effect of VE Territory Covered Losses Recovery on the Company Repurchasing its Common Stock (Details) - USD ($)		3 Months Ended	9 Months Ended
		Jun. 30, 2017	Jun. 30, 2017
Conversion of Stock [Line Items]
Recovery through conversion rate adjustment			$ (191,000,000)
U.K.& I preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of shares of class A common stock		1,000,000	2,000,000
Effective price per share (in USD per share)	[1]	$ 92.38	$ 88.70
Recovery through conversion rate adjustment		$ 71,000,000	$ 190,280,000.00
Europe preferred stock
Conversion of Stock [Line Items]
Reduction in equivalent number of shares of class A common stock	[2]		0
Effective price per share (in USD per share)	[1]		$ 85.01
Recovery through conversion rate adjustment			$ 1,000,000

[1] Effective price per share is calculated using the volume-weighted average price of the Company's class A common stock over a pricing period in accordance with the Company's current certificates of designations for its series B and C convertible participating preferred stock.

[2] The reduction in equivalent number of shares of class A common stock was less than one million shares.