Business and Summary of Significant Accounting Policies - Adoption of New Accounting Standard - Balance Sheet (Details) - USD ($) $ in Millions	Jan. 31, 2020	Feb. 01, 2019	Jan. 31, 2019
ASSETS
Prepaid expenses and other current assets	$ 163.3		$ 192.1
Total current assets	2,659.3		1,620.0
Operating lease right-of-use assets	438.8		0.0
Total assets	6,179.3		4,729.2
Current liabilities:
Other accrued liabilities	168.3		142.3
Operating lease liabilities	48.1		0.0
Long-term operating lease liabilities			0.0
Long-term other liabilities	119.8		121.8
Accumulated deficit	$ (2,295.8)		(2,147.4)
Accounting Standards Update 2016-02
ASSETS
Prepaid expenses and other current assets		$ 186.2
Total current assets		1,614.1
Operating lease right-of-use assets		283.4
Total assets		5,006.7
Current liabilities:
Other accrued liabilities		137.4
Operating lease liabilities		54.1
Long-term operating lease liabilities		245.9
Long-term other liabilities		104.9
Accumulated deficit		(2,148.1)
Restatement Adjustment | Accounting Standards Update 2016-02
ASSETS
Prepaid expenses and other current assets		(5.9)
Total current assets		(5.9)
Operating lease right-of-use assets		283.4
Total assets		277.5
Current liabilities:
Other accrued liabilities		(4.9)
Operating lease liabilities		54.1
Long-term operating lease liabilities		245.9
Long-term other liabilities		(16.9)
Accumulated deficit		$ (0.7)
As reported
ASSETS
Prepaid expenses and other current assets			192.1
Total current assets			1,620.0
Total assets			4,729.2
Current liabilities:
Other accrued liabilities			142.3
Long-term other liabilities			121.8
Accumulated deficit			$ (2,147.4)