Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Comprehensive Income (Loss), Amortization, Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Recognized in Net Periodic Benefit Cost, before Tax	[1]	$ (80.7)	$ (34.0)	$ (31.9)
Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax		(2.0)	0.0	0.0
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax		(48.5)	(56.7)	71.6
Accumulated Other Comprehensive Income (Loss), Net of Tax		(4,580.7)	(3,991.8)
Other comprehensive income (loss)		(588.9)	(1,989.1)	1,794.4
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, before Tax		340.5	269.0	483.3
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, for Net Gain (Loss), before Tax	[1]	421.2	303.0	515.2
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Tax		(105.6)	(83.4)	(164.3)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI, Pension and Other Postretirement Benefit Plans, Net of Tax		234.9	185.6	319.0
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax		(209.3)	(324.1)	(12.0)
Other Comprehensive (Income) Loss, Reclassification Adjustment from AOCI for Write-down of Securities, before Tax		12.0	0.0	2.4
Other Comprehensive Income (Loss), Reclasification Adjustment from AOCI, Available-for-Sale Securities, before Tax, Total		(197.3)	(324.1)	(9.6)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax		69.1	113.4	3.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI, Available-for-Sale Securities, Net of Tax, Total		(128.2)	(210.7)	(6.2)
Other Comprehensive Income, Other, Net of Tax		9.5	5.9	5.9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		116.2	(19.2)	318.7
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax		14.6	5.2	43.2
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, before Reclassification Adjustments, Tax		(183.0)	414.7	(886.1)
Other Comprehensive Income (Loss), Tax		(121.9)	476.6	(914.5)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(4,580.7)	(3,991.8)	(2,002.7)	$ (3,797.1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		705.1	1,969.9	(1,475.7)
Other comprehensive income (loss)		(588.9)	(1,989.1)	1,794.4
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(116.2)	19.2	(318.7)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(1,360.2)	(498.4)	463.0	426.8
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		861.8	961.4	(36.2)
Other comprehensive income (loss)		(861.8)	(961.4)	36.2
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		0.0	0.0	0.0
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax		10.1	99.7	205.2	72.5
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(38.6)	(105.2)	(138.9)
Other comprehensive income (loss)		(89.6)	(105.5)	132.7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		128.2	210.7	6.2
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(3,012.1)	(3,402.0)	(2,489.1)	(4,195.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		(155.0)	1,098.5	(1,387.1)
Other comprehensive income (loss)		389.9	(912.9)	1,706.1
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(234.9)	(185.6)	(319.0)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax		(218.5)	(191.1)	(181.8)	$ (101.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		36.9	15.2	86.5
Other comprehensive income (loss)		(27.4)	(9.3)	(80.6)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		$ (9.5)	$ (5.9)	$ (5.9)

[1] (1) These accumulated other comprehensive loss components are included in the computation of net periodic pension cost (see Note 14).