Benefit Plans (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 15, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Pension benefits
Components of net periodic cost
Decrease to unrecognized pension and other postretirement benefit cost	$ 599
Discount rate (as a percent)	4.75%					4.00%
Expected long-term rate of return on plan assets (as a percent)				7.75%
Settlement loss, pre-tax		76
Components of net periodic cost
Service cost		32	38	111	114
Interest cost		66	74	198	223
Expected return on plan assets		(100)	(98)	(293)	(295)
Amortization of prior service credit		(12)	(1)	(13)	(2)
Amortization of net actuarial loss (gain)		54	45	184	134
Settlement loss		85	10	104	29
Net periodic (credit) cost		125	68	291	203
Postretirement benefits
Components of net periodic cost
Decrease to unrecognized pension and other postretirement benefit cost	59
Discount rate (as a percent)	3.75%					4.25%
Curtailment gain, pre-tax		181
Components of net periodic cost
Service cost		3	3	10	9
Interest cost		6	9	23	27
Amortization of prior service credit		(5)	(6)	(17)	(17)
Amortization of net actuarial loss (gain)		(5)	(5)	(11)	(15)
Curtailment gain		(181)		(181)
Net periodic (credit) cost		$ (182)	$ 1	$ (176)	$ 4