Reclassifications From Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Reclassifications from accumulated other comprehensive (loss) income
Other, net	$ 4	$ 1	$ 58	$ 5
Tax (benefit) expense	(96)	(81)	(243)	(229)
Net income available to common shareholders	147	132	442	388
Actuarial losses, net
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, before tax	6	6	17	14
Amortization of defined benefit pension and other postretirement benefits
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, tax (benefit)	(2)	(3)	(6)	(5)
Reclassifications, after tax	4	3	11	9
Interest rate swaps | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Tax (benefit) expense	0	0	(1)	0
Net income available to common shareholders	0	0	2	1
Interest rate swaps | Interest rate swaps | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Interest expense	0	0	3	1
Available-for-sale securities | Reclassification from Accumulated Other Comprehensive Loss
Reclassifications from accumulated other comprehensive (loss) income
Other, net	0	0	0	(1)
Tax (benefit) expense	0	0	0	0
Net income available to common shareholders	$ 0	$ 0	$ 0	$ (1)