Employee Benefit Plans - Net Periodic Cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, service cost	$ 0	$ 0	$ 0
Defined benefit plan, interest cost	928	861	930
Defined Benefit Plan, Expected Return on Plan Assets	(829)	(734)	(705)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	0	0	0
Defined Benefit Plan, Amortization of Gains (Losses)	134	221	143
Defined Benefit Plan, Recognized Net (Gain) Loss Due to Settlements	0	6	0
Defined benefit plan, other costs	0	0	0
Defined Benefit Plan, Net Periodic Benefit Cost	233	354	368
Defined Contribution Plan, Cost Recognized	551	490	426
Defined Benefit Plan Cost Benefit	784	844	794
Other Postretirement and Postemployment Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, service cost	52	49	56
Defined benefit plan, interest cost	155	143	164
Defined Benefit Plan, Expected Return on Plan Assets	(84)	(84)	(77)
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	(26)	(26)	(21)
Defined Benefit Plan, Amortization of Gains (Losses)	4	25	23
Defined Benefit Plan, Recognized Net (Gain) Loss Due to Settlements	0	0	0
Defined benefit plan, other costs	0	0	116
Defined Benefit Plan, Net Periodic Benefit Cost	101	107	261
Defined Contribution Plan, Cost Recognized	0	0	0
Defined Benefit Plan Cost Benefit	$ 101	$ 107	$ 261