Fair Value Measurements - Fair Value of Financial Assets and Financial Liabilities (Detail) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Assets:
Investments	$ 85	$ 92
Level 1 [Member]
Assets:
Investments	15	20
Fair Value, Inputs, Level 2 [Member]
Assets:
Investments	70	72
Fair Value, Inputs, Level 3 [Member]
Assets:
Investments	0	0
Equity Securities [Member]
Assets:
Investments	15	20
Equity Securities [Member] | Level 1 [Member]
Assets:
Investments	15	20
Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Investments	0	0
Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Investments	0	0
US Treasury and Government [Member]
Assets:
Investments	70	72
US Treasury and Government [Member] | Level 1 [Member]
Assets:
Investments	0	0
US Treasury and Government [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Investments	70	72
US Treasury and Government [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Investments	$ 0	$ 0