Debt - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		1 Months Ended		3 Months Ended	9 Months Ended	60 Months Ended
	Jan. 07, 2014	Mar. 17, 2014	Nov. 30, 2006	Sep. 30, 2015	Sep. 30, 2015	Feb. 27, 2020	Nov. 06, 2015	Mar. 23, 2015	Feb. 27, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Jan. 07, 2013	Jun. 30, 2012	Dec. 31, 2010	Nov. 13, 2006
Commercial Paper				$ 1,970	$ 1,970					$ 0
Line of Credit Facility, Maximum Borrowing Capacity									$ 2,500
line of credit available increase to credit facility									$ 1,000
Convertible Senior Notes 2013
Senior Notes																$ 1,725
Stated interest rate																1.75%
Cash payment to noteholders for outstanding principal of converted Notes	$ 1,700
Shares issued to noteholders for the excess of the conversion value over the principal amount of converted Notes (in shares)	35
Value of the conversion value over the principal amount of converted Notes	$ 858
Observation period	20 days
Convertible conversion ratio	62.6978
Conversion premium	26.50%
Conversion price per share													$ 15.95
Purchased Options
Purchased Options Remaining											108
Purchased options shares received	35
Sold Warrants
Incremental common shares attributable to call options and warrants			215
Common stock at an exercise price			$ 19.55													$ 19.31
Proceeds from issuance of warrants			$ 391
Conversion premium based on the closing price			53.00%
Closing price per share																$ 12.61
Warrant
Warrants exercised		$ 109
Exercised Warrants
Shares issues for exercised warrants		29
Long-term Debt
Unamortized discount				$ 5	$ 5
Effective interest rate				2.55%	2.55%
Long-term Debt
Long term debt, aggregate principal												$ 5,500
Interest Rate Swap
Aggregate notional amount of interest rate swap contracts designated as cash flow hedges															$ 900
Losses on swaps at time of settlement, deferred														$ 176
Losses reclassified from other comprehensive income and recognized as interest expense				$ 6	$ 17
Commercial Paper
Commercial Paper Maximum Borrowing Amount								$ 2,500
Short-term Debt, Terms				The Commercial Paper will have maturities of up to 397 days from the date of issue
Short-term Debt, Weighted Average Interest Rate				0.24%	0.24%
Minimum | Commercial Paper
Short-term Debt, Terms					34
Maximum | Commercial Paper
Short-term Debt, Terms					80
Scenario, Forecast
Line of Credit Facility, Expiration Date						Feb. 27, 2020
Line of Credit Facility, Description						At our option, subject to certain conditions, any loan under the Credit Agreement will bear interest at a rate equal to, either (i) the LIBOR Rate or (ii) the Base Rate (defined as the highest of (a) the Federal Funds rate plus 0.50%, (b) Citibank, N.A.’s “prime rate” as announced from time to time, or (c) one-month LIBOR plus 1.00%), plus, in each case the Applicable Margin, as defined in the Credit Agreement
Subsequent Event
Line of Credit, Current							$ 600
Subsequent Event | Commercial Paper
Commercial Paper							$ 2,000