Income Taxes (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation of unrecognized tax benefits
Balance at the beginning of the period	$ 589	$ 278	$ 390
Increases in tax positions for prior years	47	126
Decreases in tax positions for prior years	(53)	(3)	(6)
Increases in tax positions for the current year	209	214	35
Settlements with taxing authorities	(6)	(25)
Expirations of the statute of limitations	(2)	(1)	(141)
Balance at the end of the period	784	589	278
Portion of Unrecognized tax benefits which would affect the annual effective income tax rate	669
Interest and penalties related to unrecognized tax benefits in income tax expense	12	38	12
Accrued interest and penalties for unrecognized tax benefits	$ 67	$ 70
Period for which income tax returns are subject to examination in other state and foreign tax jurisdictions	3 years