Assets and Liabilities Measured at Fair Value on a Recurring Basis (Additional Information) (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	$ 84	$ 93
Investment in Federal Home Loan Bank Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	202	32
Federal Reserve Bank Stock [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	402	402
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	$ 6	$ 6