Tangible Equity Units - Additional Information (Detail) - Jun. 30, 2015 - 7.50% Tangible Equity Units [Member] shares in Millions, $ in Millions	USD ($) shares / unit $ / unit shares
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 | $	$ 446
Purchase contract, mandatory settlement date	Jun. 07, 2018
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
Settled In APC Shares [Member]
Tangible Equity Units [Line Items]
APC share cap | shares / unit	4