New Accounting Standards Effect of Standard Change (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Mar. 31, 2017
Item Effected [Line Items]
Liabilities		$ 32,144.5	$ 27,196.5	$ 32,144.5	$ 27,196.5		$ 28,912.7
Assets		43,363.5	36,689.8	43,363.5	36,689.8		38,701.2
Provision (benefit) for income taxes		178.9	181.9	359.9	393.1
Cumulative Effect of New Accounting Principle in Period of Adoption							1,300.2
Reclassification of Stranded Amounts in AOCI to Retained Earnings							$ 4.3
Accounting Standards Update 2016-01 [Member]
Item Effected [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption						$ 1,300.0
Adjustments for New Accounting Pronouncement | Pro Forma [Member] | Property Subject to Operating Lease [Member]
Item Effected [Line Items]
Liabilities		140.0		140.0
Assets		140.0		140.0
Accounting Standards Update 2018-02 [Member]
Item Effected [Line Items]
Reclassification of Stranded Amounts in AOCI to Retained Earnings								$ 4.3
Retained Earnings | Accounting Standards Update 2016-01 [Member]
Item Effected [Line Items]
Cumulative Effect of New Accounting Principle in Period of Adoption	[1]	1,300.2	0.0	1,300.2	0.0
Retained Earnings | Accounting Standards Update 2018-02 [Member]
Item Effected [Line Items]
Reclassification of Stranded Amounts in AOCI to Retained Earnings	[1]	$ 4.3	$ 0.0	$ 4.3	$ 0.0

[1] See Note 14 – New Accounting Standards for further discussion.