Income Tax Reconciliation of the tax provision at the U.S. Federal Statutory Rate (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount	$ 3,380	$ 3,120	$ 3,018
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	35.00%	35.00%	35.00%
Nonrefundable Industry Tax Expense	469	0	0
Effective Income Tax Rate Nondeductible Industry Tax	4.80%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	154	126	143
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	1.60%	1.40%	1.70%
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount	(49)	(53)	(59)
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent	(0.50%)	(0.60%)	(0.70%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount	96	39	22
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	1.00%	0.50%	0.20%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	(13)	10	(28)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	(0.10%)	0.10%	(0.30%)
Total provision for income taxes	$ 4,037	$ 3,242	$ 3,096
Effective Income Tax Rate Reconciliation, Percent	41.80%	36.40%	35.90%