Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Sep. 30, 2016		Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[1]	Sep. 30, 2015		Jun. 30, 2015	[1]	Mar. 31, 2015	[1]	Dec. 31, 2014	[1]	Sep. 30, 2016		Sep. 30, 2015		Sep. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Recognized settlement losses	$ (2.8)	[1]	$ (1.0)		$ (2.6)		$ 0.0		$ (7.0)	[1]	$ (1.6)		$ (12.6)		$ 0.0		$ (6.4)	[1]	$ (21.2)	[1]	$ (5.5)
Shares of Common Stock in ESOP	3,031,534																3,031,534
Defined Contribution Plan, Cost Recognized																	$ 43.2		44.2		$ 45.2
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Company contributions																	79.3
ABO for all defined benefit pension plans	$ 4,954.9								$ 4,444.8								4,954.9		4,444.8
Pension arrangements not funded because of jurisdictional practice, accumulated benefit obligation	108.0																108.0
Pension arrangements not funded because of jurisdictional practice, projected benefit obligation	$ 115.3																$ 115.3
Average remaining service period																	approximately 10 years
Pension Plans, Defined Benefit [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for next fiscal year																	$ 65.0
Pension Plans, Defined Benefit [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Total expected contributions for next fiscal year																	85.0
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits paid																	$ 12.3		$ 9.3
Discount rate																	2.40%		2.60%		2.40%
Accumulated postretirement benefit obligation discount rate	1.90%								2.40%								1.90%		2.40%
Net actuarial loss	$ 18.7								$ 11.9								$ 18.7		$ 11.9
Actuarial loss estimated																	(2.3)
U.S. Lump Sum Cash Payment [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefits paid																	$ 52.9

[1] For additional information, see Note 16, Retirement Benefits.