Pension and Other Postretirement Benefits - Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension And Other Postretirement Footnote Text Details [Abstract]
Postretirement benefits liability adjustment, (increase) decrease to equity, pre-tax			$ (46)
Postretirement benefits liability adjustment, (increase) decrease to equity, after-tax	$ (20)	$ (11)	(31)	$ (23)
Pension Benefits [Member]
Change in benefit obligation [Abstract]
Service cost	0	1	1	1
Interest cost	49	52	97	103
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	0	1	1	1
Interest cost	49	52	97	103
Expected long-term return on plan assets	(67)	(66)	(133)	(132)
Amortization of net loss from past experience	18	15	35	29
Amortization of prior service cost	0	0	0	0
Settlement loss	0	0	0	6
Defined benefit plan cost	0	2	0	7
Pension And Other Postretirement Footnote Text Details [Abstract]
Expected plan contributions during remainder of current fiscal year	5		5
Pension Benefits [Member] | Maximum [Member]
Pension And Other Postretirement Footnote Text Details [Abstract]
Domestic pension plan contributions			1
Other Postretirement Benefits [Member]
Change in benefit obligation [Abstract]
Service cost	0	0	0	0
Interest cost	2	3	5	6
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	0	0	0	0
Interest cost	2	3	5	6
Expected long-term return on plan assets	0	0	0	0
Amortization of net loss from past experience	0	0	0	0
Amortization of prior service cost	0	0	(1)	(1)
Settlement loss	0	0	0	0
Defined benefit plan cost	$ 2	$ 3	$ 4	$ 5