Pension and Other Postretirement Benefits - Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension And Other Postretirement Footnote Text Details [Abstract]
Postretirement benefits liability adjustment, (increase) decrease to equity, pre-tax			$ (62)
Postretirement benefits liability adjustment, (increase) decrease to equity, after-tax	$ (11)	$ (10)	(42)	$ (33)
Pension Benefits [Member]
Change in benefit obligation [Abstract]
Service cost	1	0	2	1
Interest cost	49	52	146	155
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	1	0	2	1
Interest cost	49	52	146	155
Expected long-term return on plan assets	(66)	(65)	(199)	(197)
Amortization of net loss from past experience	17	14	52	43
Amortization of prior service cost	0	0	0	0
Settlement loss	0	0	0	6
Defined benefit plan cost	1	1	1	8
Pension And Other Postretirement Footnote Text Details [Abstract]
Expected plan contributions during remainder of current fiscal year	0		0
Pension Benefits [Member] | Maximum [Member]
Pension And Other Postretirement Footnote Text Details [Abstract]
Domestic pension plan contributions			5
Other Postretirement Benefits [Member]
Change in benefit obligation [Abstract]
Service cost	0	0	0	0
Interest cost	3	3	8	9
Components of net pension cost and other postretirement benefits cost tables detail [Abstract]
Service cost	0	0	0	0
Interest cost	3	3	8	9
Expected long-term return on plan assets	0	(1)	0	(1)
Amortization of net loss from past experience	0	0	0	0
Amortization of prior service cost	(1)	(1)	(2)	(2)
Settlement loss	0	0	0	0
Defined benefit plan cost	$ 2	$ 1	$ 6	$ 6