Other Comprehensive Income (Loss) (Reclassification) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period (net of tax)	$ 49.9	$ 26.7	$ 140.8	$ 62.8
Other, net	15.4	(49.9)	(90.1)	(188.6)
Tax (benefit) expense	261.5	36.0	749.8	460.5
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period (net of tax)	49.9	26.7	140.8	62.8
Prior service benefits, net \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of retirement benefit items:	(18.2)	(21.1)	(56.6)	(63.2)
Amortization of retirement benefit items \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of retirement benefit items:	80.0	77.1	266.6	229.4
Defined Benefit Pension and Retiree Health Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of retirement benefit items:	61.8	56.0	210.0	166.2
Tax benefit	(14.6)	(15.9)	(45.1)	(48.4)
Total reclassifications for the period (net of tax)	47.2	40.1	164.9	117.8
Unrealized net gains/losses on securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period (net of tax)	(0.2)	(23.9)	(32.8)	(70.4)
Unrealized net gains/losses on securities \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	(0.3)	(36.7)	(41.6)	(108.2)
Tax (benefit) expense	0.1	12.8	8.8	37.8
Net of tax	(0.2)	(23.9)	(32.8)	(70.4)
Other, net of tax \| Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other, net	$ 2.9	$ 10.5	$ 8.7	$ 15.4

Amount after tax of income (loss) from continuing operations including portion attributable to the noncontrolling interest.

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