Debt (Public Debt) - Additional Information (Detail) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2014 USD ($) $ / shares shares	Sep. 30, 2014 USD ($)	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) shares
Debt Instrument [Line Items]
Principal amount of convertible notes | $		$ 1,250	$ 9,065	$ 8,798
Convertible notes due date			Jul. 25, 2019
Number of shares, option exercised | shares			23.3
Par value of issued shares			$ 1
Proceeds from issuance of public debt offering | $		$ 1,238
Debt instrument redemption price percentage		101.00%
5.25% Convertible Notes Due 2014 [Member]
Debt Instrument [Line Items]
Principal amount of convertible notes | $	$ 575			$ 575
Convertible notes, interest rate	5.25%			5.25%
Convertible notes due date	Mar. 15, 2014			Mar. 15, 2014
Number of shares, option exercised | shares	89.0			89.0
Conversion rate, numerator	155.4908
Conversion rate, denominator	$ 1,000
Convertible notes, conversion price	6.43
Par value of issued shares	$ 89
5.125% Senior Notes Due 2024 [Member]
Debt Instrument [Line Items]
Convertible notes, interest rate		5.125%