Consolidated Statements of Comprehensive Income (Parenthetical) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Income tax expenses (benefits) on unrealized (losses) gains on hedging instruments	$ (1)	$ (3)	$ 2
Income tax effect on amortization of net loss and prior service cost previously recognized	6	30	26
Income tax expense (benefit) on net prior service (costs) credit arising during the period		(5)	2
Income tax expense (benefit) on net gain(loss) arising during the period	$ (211)	$ 243	$ (105)