Significant Accounting Policies Schedule of New Accounting Pronouncements (Details) $ in Millions	Dec. 31, 2017 USD ($)
Accounting Standards Update 2016-01
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 0.0
Accounting Standards Update 2018-02
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	0.0
Retained Earnings | Accounting Standards Update 2016-01
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	17.0
AOCI Attributable to Parent | Accounting Standards Update 2016-01
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	(17.0)
Minimum | Retained Earnings | Accounting Standards Update 2018-02
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	(65.0)
Minimum | AOCI Attributable to Parent | Accounting Standards Update 2018-02
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	65.0
Maximum | Retained Earnings | Accounting Standards Update 2018-02
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	(85.0)
Maximum | AOCI Attributable to Parent | Accounting Standards Update 2018-02
Item Effected
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 85.0