Investments Equity Securities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Equity securities - cost	$ 2,472.9	$ 2,404.9
Available-for-sale Securities, Equity Securities	3,012.2	2,896.1
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Equity securities - cost	2,472.9	2,404.9
Equity securities, gross unrealized gains	566.8	516.2
Equity securities, gross unrealized losses	27.6	25.0
Available-for-sale Securities, Equity Securities	$ 3,012.2	$ 2,896.1