Other Comprehensive Income/(Loss) (Accumulated other comprehensive income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other comprehensive income/(loss) before tax:
Currency translation differences on investments in foreign subsidiaries	$ (364.4)	$ (121.9)	$ 145.0
Actuarial (loss)/gain related to employee benefit plans	(29.8)	7.0	(4.8)
Prior service credit related to employee benefit plans	23.5	0	0
Reclassification of amortization of prior service costs/(credit) into employee compensation expense	(6.5)	(1.9)	(2.0)
Reclassification of amortization of actuarial (gains)/losses into employee compensation expense	1.8	2.3	2.4
Share of other comprehensive income/(loss) of equity method investments	8.3	(3.9)	6.4
Unrealized(losses)/gains on available-for-sale investments	2.9	13.6	14.0
Reclassification of net (gains)/losses realized on available-for-sale investments included in other gains and losses, net	(12.8)	(3.2)	(3.9)
Other comprehensive income/(loss), before tax	(377.0)	(108.0)	157.1
Income tax related to items of other comprehensive income/(loss):
Tax benefit/(expense) on foreign currency translation adjustments	0	(0.4)	0.6
Tax on actuarial (loss)/gain related to employee benefit plans	3.8	(5.8)	(0.1)
Prior service credit related to employee benefit plans, Tax	(8.6)	0	0
Reclassification of tax on amortization of prior service costs/(credit) into income tax provision	2.4	0.4	0.5
Reclassification of tax on amortization of actuarial (loss)/gain into income tax provision	(0.4)	(0.5)	(0.6)
Tax on net unrealized gains/(losses) on available-for-sale investments	4.8	(0.5)	(1.0)
Reclassification of tax on net (gains)/losses on available-for-sale investments	(4.1)	(0.9)	(0.2)
Total income tax benefit/(expense) related to items of other comprehensive income	(2.1)	(7.7)	(0.8)
Accumulated other comprehensive income/(loss), net of tax:
Beginning balance	427.9	530.5	373.3
Other comprehensive income/(loss), net of tax:	(379.1)	(115.7)	156.3
Other comprehensive (income)/loss attributable to noncontrolling interest	0	13.1	0.9
Ending balance	48.8	427.9	530.5
Foreign currency translation [Member]
Other comprehensive income/(loss) before tax:
Currency translation differences on investments in foreign subsidiaries	(364.4)	(121.9)	145.0
Other comprehensive income/(loss), before tax	(364.4)	(121.9)	145.0
Income tax related to items of other comprehensive income/(loss):
Tax benefit/(expense) on foreign currency translation adjustments	0	(0.4)	0.6
Total income tax benefit/(expense) related to items of other comprehensive income	0	(0.4)	0.6
Accumulated other comprehensive income/(loss), net of tax:
Beginning balance	492.5	601.7	455.2
Other comprehensive income/(loss), net of tax:	(364.4)	(122.3)	145.6
Other comprehensive (income)/loss attributable to noncontrolling interest	0	13.1	0.9
Ending balance	128.1	492.5	601.7
Employee benefit plans [Member]
Other comprehensive income/(loss) before tax:
Actuarial (loss)/gain related to employee benefit plans	(29.8)	7.0	(4.8)
Prior service credit related to employee benefit plans	23.5
Reclassification of amortization of prior service costs/(credit) into employee compensation expense	(6.5)	(1.9)	(2.0)
Reclassification of amortization of actuarial (gains)/losses into employee compensation expense	1.8	2.3	2.4
Other comprehensive income/(loss), before tax	(11.0)	7.4	(4.4)
Income tax related to items of other comprehensive income/(loss):
Tax on actuarial (loss)/gain related to employee benefit plans	3.8	(5.8)	(0.1)
Prior service credit related to employee benefit plans, Tax	(8.6)
Reclassification of tax on amortization of prior service costs/(credit) into income tax provision	2.4	0.4	0.5
Reclassification of tax on amortization of actuarial (loss)/gain into income tax provision	(0.4)	(0.5)	(0.6)
Total income tax benefit/(expense) related to items of other comprehensive income	(2.8)	(5.9)	(0.2)
Accumulated other comprehensive income/(loss), net of tax:
Beginning balance	(77.9)	(79.4)	(74.8)
Other comprehensive income/(loss), net of tax:	(13.8)	1.5	(4.6)
Other comprehensive (income)/loss attributable to noncontrolling interest	0	0	0
Ending balance	(91.7)	(77.9)	(79.4)
Equity method investments [Member]
Other comprehensive income/(loss) before tax:
Share of other comprehensive income/(loss) of equity method investments	8.3	(3.9)	6.4
Other comprehensive income/(loss), before tax	8.3	(3.9)	6.4
Income tax related to items of other comprehensive income/(loss):
Total income tax benefit/(expense) related to items of other comprehensive income	0	0	0
Accumulated other comprehensive income/(loss), net of tax:
Beginning balance	(1.8)	2.1	(4.3)
Other comprehensive income/(loss), net of tax:	8.3	(3.9)	6.4
Other comprehensive (income)/loss attributable to noncontrolling interest	0	0	0
Ending balance	6.5	(1.8)	2.1
Available-for-sale investments [Member]
Other comprehensive income/(loss) before tax:
Unrealized(losses)/gains on available-for-sale investments	2.9	13.6	14.0
Reclassification of net (gains)/losses realized on available-for-sale investments included in other gains and losses, net	(12.8)	(3.2)	(3.9)
Other comprehensive income/(loss), before tax	(9.9)	10.4	10.1
Income tax related to items of other comprehensive income/(loss):
Tax on net unrealized gains/(losses) on available-for-sale investments	4.8	(0.5)	(1.0)
Reclassification of tax on net (gains)/losses on available-for-sale investments	(4.1)	(0.9)	(0.2)
Total income tax benefit/(expense) related to items of other comprehensive income	0.7	(1.4)	(1.2)
Accumulated other comprehensive income/(loss), net of tax:
Beginning balance	15.1	6.1	(2.8)
Other comprehensive income/(loss), net of tax:	(9.2)	9.0	8.9
Other comprehensive (income)/loss attributable to noncontrolling interest	0	0	0
Ending balance	$ 5.9	$ 15.1	$ 6.1