Equity - Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	$ 3,828	$ 3,613	$ 3,391
Balance	3,975	3,828	3,613
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(6)	1	(3)
OCI, before reclassifications	0	(6)	1
Amounts reclassified from accumulated OCI	8	(1)	3
Balance	2	(6)	1
Retirement Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(200)	(137)	(215)
OCI, before reclassifications	0	(71)	66
Amounts reclassified from accumulated OCI	12	8	12
Balance	(188)	(200)	(137)
Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(206)	(136)	(218)
OCI, before reclassifications	0	(77)	67
Amounts reclassified from accumulated OCI	20	7	15
Balance	$ (186)	$ (206)	$ (136)