Employee Benefit Plans, Pre-Tax Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net (gain) loss reclassified into income:
Total changes in other comprehensive income (loss)	$ (65)	$ (98)	$ 57
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(73)	(145)	24
Prior service cost	(4)	0	(22)
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	53	49	62
Prior service credit	(20)	(20)	(22)
Curtailment and settlement loss	4	0	7
Total changes in other comprehensive income (loss)	(40)	(116)	49
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(6)	35	26
Prior service cost	0	0	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	(3)	(1)	0
Prior service credit	(16)	(16)	(18)
Curtailment and settlement loss	0	0	0
Total changes in other comprehensive income (loss)	$ (25)	$ 18	$ 8