Income Taxes (Reconciliation Between Provision for Income Taxes and Amount Computed by Applying Federal Statutory Income Tax Rate) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Taxes Abstract
Federal income taxes at statutory rate of 35%	$ 1,045	$ 1,093	$ 977
State income taxes, net of Federal tax benefit	61	86	61
Federal tax credits	(171)	(152)	(126)
Tax exempt income	(125)	(128)	(133)
Adjustments to uncertain tax positions	(39)	516	0
Other, net	(11)	(20)	(15)
Provision for income taxes	$ 760	$ 1,395	$ 764
Effective income tax rate	25.50%	44.70%	27.40%