Significant Accounting Policies Schedule of New Accounting Pronouncements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle
Other Noncash Income (Expense)	$ (46.6)	$ (27.5)	$ (38.4)
Proceeds from Sales and Maturities of Other Investments	454.0	257.9	331.3
Compensation Expense	885.9	852.3	839.1
Other Expenses	891.2	855.0	824.6
Other Long-term Investments	702.9	646.8
Deferred Income Tax	0.0	199.0
Accumulated Other Comprehensive Income (Loss)	(814.2)	127.5
Retained Earnings	$ 9,863.1	9,542.2
Accounting Standards Update 2016-15
New Accounting Pronouncements or Change in Accounting Principle
Other Noncash Income (Expense)		27.5	38.4
Proceeds from Sales and Maturities of Other Investments		257.9	331.3
Accounting Standards Update 2016-15 | Historical Accounting Method
New Accounting Pronouncements or Change in Accounting Principle
Other Noncash Income (Expense)		12.8	32.9
Proceeds from Sales and Maturities of Other Investments		272.6	336.8
Accounting Standards Update 2016-15 | Effect of Change
New Accounting Pronouncements or Change in Accounting Principle
Other Noncash Income (Expense)		14.7	5.5
Proceeds from Sales and Maturities of Other Investments		(14.7)	(5.5)
Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle
Compensation Expense		852.3	839.1
Other Expenses		855.0	824.6
Accounting Standards Update 2017-07 | Historical Accounting Method
New Accounting Pronouncements or Change in Accounting Principle
Compensation Expense		844.4	832.1
Other Expenses		862.9	831.6
Accounting Standards Update 2017-07 | Effect of Change
New Accounting Pronouncements or Change in Accounting Principle
Compensation Expense		7.9	7.0
Other Expenses		(7.9)	$ (7.0)
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle
Other Long-term Investments		646.8		$ 643.0
Deferred Income Tax		199.0		198.2
Accumulated Other Comprehensive Income (Loss)		127.5		110.0
Retained Earnings		$ 9,542.2		9,556.7
Accounting Standards Update 2016-01 | Effect of Change
New Accounting Pronouncements or Change in Accounting Principle
Other Long-term Investments				(3.8)
Deferred Income Tax				(0.8)
Accumulated Other Comprehensive Income (Loss)				(17.5)
Retained Earnings				$ 14.5