Taxation (Income Before Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	$ 1,206.6	$ 1,362.1	$ 1,395.1
Domestic Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	539.9	687.9	722.6
Foreign Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	666.7	674.2	672.5
Separate Institutional Accounts [Member] | Domestic Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	537.5	661.9	659.6
Separate Institutional Accounts [Member] | Foreign Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	652.0	746.3	724.4
Consolidated Investment Products [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	17.1	(46.1)	11.1
Consolidated Investment Products [Member] | Domestic Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	2.4	26.0	63.0
Consolidated Investment Products [Member] | Foreign Tax Authority [Member]
Schedule of Income Before Taxes, Domestic and Foreign [Line Items]
Income (Loss) from Continuing Operations before Income Taxes, Extraordinary Items, Noncontrolling Interest	$ 14.7	$ (72.1)	$ (51.9)