Employee Benefit Plans (Components of Net Periodic Benefit Cost Included in General and Administrative Expenses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 61	$ 58	$ 183	$ 176
Interest cost	118	120	352	361
Expected return on plan assets	(194)	(178)	(581)	(534)
Amortization of prior service cost	(2)	(2)	(6)	(7)
Amortization of actuarial (gain) loss, net	42	22	126	65
Settlements	1	4	2	6
Special termination benefits	0	0	4	0
Net periodic (benefit) cost	26	24	80	67
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	15	13
Interest cost	21	24	64	72
Expected return on plan assets	(29)	(29)	(86)	(87)
Amortization of prior service cost	(1)	(2)	(4)	(8)
Amortization of actuarial (gain) loss, net	10	5	29	19
Settlements	0	0	0	0
Special termination benefits	0	0	0	0
Net periodic (benefit) cost	$ 6	$ 3	$ 18	$ 9