Tangible Equity Units - Additional Information (Detail) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) shares / unit $ / unit shares
Tangible Equity Units - senior amortizing notes [Member] | Senior Notes [Member]
Tangible Equity Units [Line Items]
Tangible equity unit rate	7.50%
Principal amount per amortizing note	10.95
Debt instrument, stated interest rate	1.50%
Beginning date of quarterly cash installment payments	Sep. 07, 2015
Quarterly cash installment payment per amortizing note	0.9375
First quarterly cash installment payment per amortizing note	0.9063
Debt instrument, maturity date	Jun. 07, 2018
7.50% Tangible Equity Units [Member]
Tangible Equity Units [Line Items]
Number of tangible equity units issued | shares	9.2
Tangible equity unit rate	7.50%
Stated amount per tangible equity unit	50.00
Total net proceeds | $	$ 445
Equity Component of 7.5% Tangible Equity Units [Member]
Tangible Equity Units [Line Items]
Purchase contract, mandatory settlement date	Jun. 07, 2018
Equity Component of 7.5% Tangible Equity Units [Member] | Settled In APC Shares [Member]
Tangible Equity Units [Line Items]
APC share cap | shares / unit	4