Retirement Benefits (Details 5) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Investments measured at fair value
Defined benefit plan fair value of plan assets	$ 3,788.3	$ 3,447.9
U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	2,890.1	2,616.2
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	2,779.2	2,502.2
Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	898.2	831.7
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	888.7	822.5
Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	1,389.9	1,165.0
Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	61.8	60.5
Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	1,388.4	1,336.3
Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	750.6	677.5
Fair Value, Inputs, Level 3 [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	77.2	85.4	$ 69.1
Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.9	0.9
Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	76.3	84.5
Cash and Cash Equivalents [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	1.1	2.9
Cash and Cash Equivalents [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	3.3	1.9
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	1.1	2.9
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	3.3	1.9
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Mutual funds [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	230.1	203.6
Mutual funds [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	230.1	203.6
Mutual funds [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Mutual funds [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Common stock [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	911.7	705.9
Common stock [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	57.3	48.6
Common stock [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	911.7	705.9
Common stock [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	57.3	48.6
Common stock [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Common stock [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Common stock [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Common stock [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Equity Common collective trusts [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	411.2	483.6
Equity Common collective trusts [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	311.1	279.3
Equity Common collective trusts [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Equity Common collective trusts [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	411.2	483.6
Equity Common collective trusts [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	311.1	279.3
Equity Common collective trusts [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Equity Common collective trusts [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Corporate debt [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	663.7	591.8
Corporate debt [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	37.0	34.1
Corporate debt [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Corporate debt [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Corporate debt [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	663.7	591.8
Corporate debt [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	37.0	34.1
Corporate debt [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Corporate debt [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
U.S. Government Securities [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	356.4	352.1
U.S. Government Securities [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	247.0	252.6
U.S. Government Securities [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	109.4	99.5
U.S. Government Securities [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Non-U.S. Government securities [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	16.0	17.6
Non-U.S. Government securities [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	1.2	10.0
Non-U.S. Government securities [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	14.8	7.6
Non-U.S. Government securities [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Fixed income securities Common collective trusts [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	204.1	161.4
Fixed income securities Common collective trusts [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	301.1	271.1
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	204.1	161.4
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	301.1	271.1
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Fixed income securities Common collective trusts [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Private equity [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	49.9	57.1
Alternative equity [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	61.0	56.9
Insurance contracts [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.9	0.9
Insurance contracts [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	71.5	79.7
Insurance contracts [Member] | Fair Value, Inputs, Level 1 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Insurance contracts [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Insurance contracts [Member] | Fair Value, Inputs, Level 2 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Insurance contracts [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Insurance contracts [Member] | Fair Value, Inputs, Level 3 [Member] | U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	0.9	0.9	0.9
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.9	0.9
Insurance contracts [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	71.5	79.7	63.8
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	71.5	79.7
Other [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	4.8	4.8
Other [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Other [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Other [Member] | Fair Value, Inputs, Level 3 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	4.8	4.8	$ 4.4
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	4.8	4.8
Real Estate Funds [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan fair value of plan assets	9.5	9.2
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	86.6	85.4
Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	0.0	0.0
Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member] | Non-U.S. Pension Benefit Plans [Member]
Investments measured at fair value
Defined benefit plan, fair value of plan assets excluding those measured using the NAV practical expedient	$ 86.6	$ 85.4