Reclassifications From Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassifications from accumulated other comprehensive (loss) income
Other, net	$ 51	$ 5	$ 54	$ 4
Tax (benefit) expense	(84)	(90)	(147)	(148)
Net income available to common shareholders	157	148	295	256
Actuarial losses, net
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, before tax	5	3	11	8
Amortization of defined benefit pension and other postretirement benefits
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, tax (benefit)	(2)	0	(4)	(2)
Reclassifications, after tax	3	3	7	6
Interest rate swaps | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Tax (benefit) expense	(1)	0	(1)	0
Net income available to common shareholders	2	1	2	1
Interest rate swaps | Interest rate swaps | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Interest expense	3	1	3	1
Available-for-sale securities | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Other, net	0	(1)	0	(1)
Tax (benefit) expense	0	0	0	0
Net income available to common shareholders	$ 0	$ (1)	$ 0	$ (1)