Long-term Debt (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Long-term Debt, by Current and Noncurrent [Abstract]
Premiums paid to extinguish debt			$ 2,067	$ 0
Gain (Loss) on Extinguishment of Debt	$ (1,344)	$ 0	$ (2,132)	$ 0