Stock-Based Compensation - Stock options (Details) - Stock options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Weighted-average assumptions utilized in determining the fair value of options
Risk-free interest rate (as a percent)	2.20%	2.00%
Expected stock volatility (as a percent)	36.10%	39.40%
Dividend yield (as a percent)	4.80%	3.40%
Expected term (in years)	6 years	5 years 6 months
Options
Options outstanding at the beginning of the period (in shares)	3,278
Granted (in shares)	660
Exercised (in shares)	(183)
Option outstanding at the end of the period (in shares)	3,755
Vested and expected to vest at the end of the period (in shares)	3,755
Exercisable at the end of the period (in shares)	2,388
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share)	$ 56.41
Granted (in dollars per share)	58.52
Exercised (in dollars per share)	35.07
Outstanding at the end of the period (in dollars per share)	57.82
Vested and expected to vest at the end of the period (in dollars per share)	57.82
Exercisable at the end of the period (in dollars per share)	$ 55.15
Weighted- Average Remaining Contractual Term
Outstanding at the end of the period	6 years 5 months 5 days
Vested and expected to vest at the end of the period	6 years 5 months 5 days
Weighted-average remaining life of exercisable stock options	4 years 11 months 1 day
Aggregate Intrinsic Value
Outstanding at the end of the period (in dollars)	$ 36.1
Options vested or expected to vest, aggregate intrinsic value (in dollars)	36.1
Exercisable at the end of the period (in dollars)	$ 29.2