Other–Net, (Income) Expense (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Nonoperating Income (Expense) [Abstract]
Interest expense	$ 83.6	$ 89.6	$ 258.4	$ 270.4
Interest income	(7.0)	(5.8)	(18.0)	(27.2)
Net investment gains	246.8	(141.7)	(270.1)	(905.1)
Retirement benefit plans	(72.6)	(114.0)	(217.1)	(194.5)
Debt extinguishment loss (Note 6)	405.2	0.0	405.2	0.0
Other (income) expense	(20.1)	13.0	(34.1)	161.5
Other–net, (income) expense	$ 635.9	$ (158.9)	$ 124.3	$ (694.9)

Amount of unrealized and realized gain (loss) on investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Amount before accretion (amortization) of purchase discount (premium) of interest income on nonoperating securities.

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Amount of expense (reversal of expense) for net periodic benefit cost components, excluding service cost component, of defined benefit plan. Amount includes, but is not limited to, interest cost, expected (return) loss on plan asset, amortization of prior service cost (credit), amortization of (gain) loss, amortization of transition (asset) obligation, settlement (gain) loss, curtailment (gain) loss and certain termination benefits.

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The aggregate amount of income or expense from ancillary business-related activities (that is to say, excluding major activities considered part of the normal operations of the business).

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Amount of income (expense) related to nonoperating activities, classified as other.

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