Income Taxes - Provision for Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Federal:
Current	$ 955us-gaap_CurrentFederalTaxExpenseBenefit	$ 698us-gaap_CurrentFederalTaxExpenseBenefit	$ 792us-gaap_CurrentFederalTaxExpenseBenefit
Deferred	(308)	(163)	(80)
Federal, total	647	535	712
State:
Current	81	84	74
Deferred	(70)	(23)	(12)
State, total	11	61	62
Foreign:
Current	228us-gaap_CurrentForeignTaxExpenseBenefit	192us-gaap_CurrentForeignTaxExpenseBenefit	169us-gaap_CurrentForeignTaxExpenseBenefit
Deferred	(18)	(16)	(25)
Foreign, total	210	176	144
Total provision for income taxes	$ 868us-gaap_IncomeTaxExpenseBenefit	$ 772us-gaap_IncomeTaxExpenseBenefit	$ 918us-gaap_IncomeTaxExpenseBenefit

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