Reclassifications From Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, tax (benefit)		$ 59
Income Tax Expense (Benefit)	$ 88		$ 86	$ 127	$ 148
Net income available to common shareholders	210		161	357	298
Actuarial losses, net
Reclassifications from accumulated other comprehensive (loss) income
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	5		5	10	11
Amortization of defined benefit pension and other postretirement benefits
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, tax (benefit)	(2)		(2)	(2)	(4)
Reclassifications, after tax	3		3	8	7
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassifications from accumulated other comprehensive (loss) income
Income Tax Expense (Benefit)	0		(1)	0	(1)
Net income available to common shareholders	1		2	1	2
Interest rate swaps | Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Including Portion Attributable to Noncontrolling Interest [Member]
Reclassifications from accumulated other comprehensive (loss) income
Interest expense	$ 1		$ 3	$ 1	$ 3