Other Comprehensive Income (Loss) (Roll-forward) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		$ 14,080.5
Other comprehensive income (loss) before reclassifications		114.0	$ (895.8)	$ (705.1)
Net amount reclassified from accumulated other comprehensive loss		60.5	250.7	116.2
Net other comprehensive income (loss)	[1]	174.5	(645.1)	(588.9)
Ending balance		11,667.9	14,080.5
Accumulated other comprehensive loss		5,718.6	5,274.0
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(5,225.8)	(4,580.7)	(3,991.8)
Reclassifications of stranded tax effects - provisional (Note 2)		(643.6)
Ending balance		(5,694.9)	(5,225.8)	(4,580.7)
Foreign Currency Translation Gains (Losses)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(1,867.3)	(1,360.2)	(498.4)
Other comprehensive income (loss) before reclassifications		664.6	(581.6)	(861.8)
Net amount reclassified from accumulated other comprehensive loss		8.1	74.5	0.0
Net other comprehensive income (loss)		672.7	(507.1)	(861.8)
Reclassifications of stranded tax effects - provisional (Note 2)		(38.8)
Ending balance		(1,233.4)	(1,867.3)	(1,360.2)
Unrealized Net Gains (Losses) on Securities
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		224.0	10.1	99.7
Other comprehensive income (loss) before reclassifications		(15.7)	206.7	38.6
Net amount reclassified from accumulated other comprehensive loss		(110.6)	7.2	(128.2)
Net other comprehensive income (loss)		(126.3)	213.9	(89.6)
Reclassifications of stranded tax effects - provisional (Note 2)		15.8
Ending balance		113.5	224.0	10.1
Effective Portion of Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(210.9)	(218.5)	(191.1)
Other comprehensive income (loss) before reclassifications		8.5	(2.2)	(36.9)
Net amount reclassified from accumulated other comprehensive loss		9.6	9.8	9.5
Net other comprehensive income (loss)		18.1	7.6	(27.4)
Reclassifications of stranded tax effects - provisional (Note 2)		(41.5)
Ending balance		(234.3)	(210.9)	(218.5)
Defined Benefit Pension and Retiree Health Benefit Plans
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance		(3,371.6)	(3,012.1)	(3,402.0)
Other comprehensive income (loss) before reclassifications		(543.4)	(518.7)	155.0
Net amount reclassified from accumulated other comprehensive loss		153.4	159.2	234.9
Net other comprehensive income (loss)		(390.0)	(359.5)	389.9
Reclassifications of stranded tax effects - provisional (Note 2)		(579.1)
Ending balance		(4,340.7)	(3,371.6)	$ (3,012.1)
Accumulated Other Comprehensive Loss
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Reclassifications of stranded tax effects - provisional (Note 2)		(643.6)
Accumulated other comprehensive loss		5,718.6	5,274.0
AOCI Attributable to Noncontrolling Interest
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Accumulated other comprehensive loss		$ (23.7)	$ (48.2)

[1] Other comprehensive loss in 2016 consists of $693.3 million of other comprehensive loss attributable to controlling interest and $48.2 million of other comprehensive income attributable to non-controlling interest. Other comprehensive income in 2017 consists of $199.0 million of other comprehensive income attributable to controlling interest and $24.5 million of other comprehensive loss attributable to non-controlling interest.