Retirement Benefits (Schedule of Fair Value Disclosures) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	$ 12,858.0	$ 10,932.6	$ 11,713.0
Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,768.2	2,398.1	$ 2,372.4
U.S. | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	794.2	617.7
U.S. | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	76.5	59.9
International | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,439.2	2,117.8
International | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	152.6	127.0
Developed markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	3,661.4	2,933.4
Developed markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	82.7	69.1
Developed markets - repurchase agreements | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	(1,659.1)	(1,225.5)
Emerging markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	648.0	565.2
Emerging markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	58.5	53.5
Hedge funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,897.9	2,795.3
Hedge funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	250.8	245.8
Equity-like funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,279.3	1,893.5
Equity-like funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	187.4	169.2
Cash value of trust owned insurance contract | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,832.2	1,574.7
Real estate | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	570.3	505.7
Real estate | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	31.3	27.7
Other | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,226.8	729.5
Other | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	96.2	71.2
Quoted Prices in Active Markets for Identical Assets (Level 1) | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,831.7	1,618.6
Quoted Prices in Active Markets for Identical Assets (Level 1) | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	140.5	144.3
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	532.5	409.1
Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	52.1	41.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | International | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,046.8	828.8
Quoted Prices in Active Markets for Identical Assets (Level 1) | International | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	60.8	50.5
Quoted Prices in Active Markets for Identical Assets (Level 1) | Developed markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	4.8	17.2
Quoted Prices in Active Markets for Identical Assets (Level 1) | Developed markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Developed markets - repurchase agreements | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	18.5	3.4
Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Hedge funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Hedge funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity-like funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity-like funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash value of trust owned insurance contract | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	166.2	147.1
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real estate | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	16.2	14.7
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	62.9	213.0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Other | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	11.4	38.1
Significant Other Observable Inputs (Level 2) | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,499.8	1,287.3
Significant Other Observable Inputs (Level 2) | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,923.4	1,657.9
Significant Other Observable Inputs (Level 2) | U.S. | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | U.S. | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | International | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | International | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Developed markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,658.9	2,173.3
Significant Other Observable Inputs (Level 2) | Developed markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	56.3	61.5
Significant Other Observable Inputs (Level 2) | Developed markets - repurchase agreements | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	(1,659.1)	(1,225.5)
Significant Other Observable Inputs (Level 2) | Emerging markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	277.4	255.8
Significant Other Observable Inputs (Level 2) | Emerging markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	27.0	25.5
Significant Other Observable Inputs (Level 2) | Hedge funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Hedge funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Equity-like funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Equity-like funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Cash value of trust owned insurance contract | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,832.2	1,574.7
Significant Other Observable Inputs (Level 2) | Real estate | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Real estate | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Other Observable Inputs (Level 2) | Other | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	222.6	83.7
Significant Other Observable Inputs (Level 2) | Other | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	7.9	(3.8)
Significant Unobservable Inputs (Level 3) | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	27.5	24.7
Significant Unobservable Inputs (Level 3) | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2.7	2.5
Significant Unobservable Inputs (Level 3) | U.S. | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | U.S. | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | International | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	1.8
Significant Unobservable Inputs (Level 3) | International | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.2
Significant Unobservable Inputs (Level 3) | Developed markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Developed markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Developed markets - repurchase agreements | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Emerging markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	4.1	6.1
Significant Unobservable Inputs (Level 3) | Emerging markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.4	0.6
Significant Unobservable Inputs (Level 3) | Hedge funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Hedge funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Equity-like funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	16.8	16.8
Significant Unobservable Inputs (Level 3) | Equity-like funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1.6	1.7
Significant Unobservable Inputs (Level 3) | Cash value of trust owned insurance contract | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Real estate | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Real estate | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Significant Unobservable Inputs (Level 3) | Other | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	6.6	0.0
Significant Unobservable Inputs (Level 3) | Other | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.7	0.0
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	9,499.0	8,002.0
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	701.6	593.4
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | U.S. | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	261.7	208.6
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | U.S. | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	24.4	18.9
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | International | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	1,392.4	1,287.2
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | International | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	91.8	76.3
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Developed markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	997.7	742.9
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Developed markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	26.4	7.6
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Developed markets - repurchase agreements | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Emerging markets | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	348.0	299.9
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Emerging markets | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	31.1	27.4
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Hedge funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,897.9	2,795.3
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Hedge funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	250.8	245.8
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Equity-like funds | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	2,262.5	1,876.7
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Equity-like funds | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	185.8	167.5
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Cash value of trust owned insurance contract | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	0.0	0.0
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Real estate | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	404.1	358.6
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Real estate | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	15.1	13.0
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Other | Defined Benefit Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	934.7	432.8
Fair Value, Retirement Benefits, Investments Valued at Net Asset Value | Other | Retiree Health Benefit Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Line Items]
Fair value of plan assets	$ 76.2	$ 36.9