Financial Instruments Available for Sale Securities Gain/Loss Activity (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Investments, All Other Investments [Abstract]
Cost method investments	$ 108,500,000		$ 108,500,000		$ 117,200,000
Other than temporary impairment losses, investments	$ 3,600,000	$ 300,000	4,100,000	$ 300,000
Gain (loss) from sale or redemption of available for sale securities			0	400,000
Proceeds from sale and maturity of marketable securities			$ 531,100,000	$ 1,146,000,000