Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Discrete income tax benefits	$ 587.6
Discrete deferred income tax benefit	897.6
Discrete current income tax expense	310.0
Unrecognized tax benefits	249.0
Unrecognized tax benefits, net of federal benefit	223.9
Tax benefits that would reduce income tax expense and effective tax rate	205.6
Unrecognized tax benefits - interest and penalties	15.4
Unrecognized tax benefits - increase (decrease)	89.4
Significant change in unrecognized tax benefits is reasonably possible	$ 5.3
Effective tax rate	(140.10%)	31.90%