Equity - Reclassification out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income (expense)									$ 497.4	$ 83.3	$ 11.0
Income tax benefit (expense)									992.3	1,158.0	1,425.6
Revenues	$ 2,852.6	$ 3,376.1	$ 3,681.6	$ 3,534.3	$ 3,671.3	$ 3,600.1	$ 3,616.7	$ 3,489.8	13,444.6	14,377.9	13,452.9
Total reclassifications, net of tax	$ 357.9	$ 701.5	$ 1,542.1	$ 1,399.1	$ 1,439.7	$ 1,545.9	$ 1,494.1	$ 1,408.8	4,000.6	5,888.5	4,430.7
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Total reclassifications, net of tax									18.2	125.6	(47.0)
Gains (losses) on securities available for sale | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income (expense)									(8.2)	4.5	(8.5)
Income tax benefit (expense)									1.7	(0.9)	1.8
Gains (losses) on cash flow hedges | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income (expense)									0.3	0.3	0.3
Income tax benefit (expense)									(0.1)	(0.6)	0.2
Revenues									18.3	118.6	(42.5)
Operating expenses									3.3	(3.3)	0.2
Gains (losses) on net investment hedge | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income on Derivatives [Line Items]
Other income (expense)									$ 2.9	$ 7.0	$ 1.5