Lease In/Lease Out Transactions - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2013	Jan. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Operating Leased Assets [Line Items]
Estimated charge after-tax	$ 150
Reduced interest expense			13	5
Uncertain tax positions, net of tax			7
Defray of interest charges relating to potential tax liability		447
Refund from IRS					10
Settlement of tax and interest					38
Transaction One [Member]
Operating Leased Assets [Line Items]
Returned deposit from IRS					125
Transaction Two [Member]
Operating Leased Assets [Line Items]
Returned deposit from IRS					$ 48