Equity - Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance			$ 3,975	$ 3,828
Other comprehensive (loss) income, net of tax	$ (8)	$ 33	(35)	38
Balance	3,933	3,989	3,933	3,989
Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(28)	(4)	2	(6)
OCI, before reclassifications	(12)	25	(41)	27
Amounts reclassified from accumulated OCI	2	3	1	3
Other comprehensive (loss) income, net of tax	(10)	28	(40)	30
Balance	(38)	24	(38)	24
Retirement Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(185)	(197)	(188)	(200)
OCI, before reclassifications	0	0	0	0
Amounts reclassified from accumulated OCI	2	4	5	7
Other comprehensive (loss) income, net of tax	2	4	5	7
Balance	(183)	(193)	(183)	(193)
Total [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance	(213)	(201)	(186)	(206)
OCI, before reclassifications	(12)	25	(41)	27
Amounts reclassified from accumulated OCI	4	7	6	10
Other comprehensive (loss) income, net of tax	(8)	32	(35)	37
Balance	$ (221)	$ (169)	$ (221)	$ (169)