Postretirement Benefit Plans (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Change in benefit obligation:
Plan amendment	$ 10
Benefit obligation at end of year		930	840
Other postretirement benefit plans
Change in benefit obligation:
Benefit obligation at beginning of year		63	65
Service cost		1	1	1
Interest cost		3	3	3
Benefits paid		(3)	(3)
Actuarial loss (gain)		12	(2)
Plan amendment		18	0
Other		0	(1)
Benefit obligation at end of year		$ 58	$ 63	$ 65