Fair Value - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Transfers between Level 1 and Level 2	$ 0			$ 0
Level 3 assets fair value	37	37	37	36	38	38
Upper limit percentage of Level 3 assets to total invested assets	0.40%
Long-term debt, carrying value	2,595		2,600
Long-term debt, fair value	$ 2,850		$ 2,751