Reclassifications From Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Reclassifications from accumulated other comprehensive (loss) income
Reclassifications, tax (benefit)		$ 59
Income Tax Expense (Benefit)	$ 71		$ 100	$ 198	$ 248
Net income available to common shareholders	179		151	535	449
Actuarial losses, net
Reclassifications from accumulated other comprehensive (loss) income
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	5		6	15	17
Reclassifications, tax (benefit)	(1)		(2)	(3)	(6)
Reclassifications, after tax	4		4	12	11
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		0	0	(1)
Net income available to common shareholders	0		0	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	$ 0		$ 0	$ 1	$ 3