Fair Value Measurements - Fair Value of Financial Assets and Financial Liabilities (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Investments, Fair Value Disclosure	$ 72	$ 85
Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	4	15
Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	68	70
Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member]
Investments, Fair Value Disclosure	4	15
Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	4	15
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member]
Investments, Fair Value Disclosure	68	70
US Treasury and Government [Member] | Fair Value, Inputs, Level 1 [Member]
Investments, Fair Value Disclosure	0	0
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Investments, Fair Value Disclosure	68	70
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Investments, Fair Value Disclosure	$ 0	$ 0