Employee Benefits - Net Pension Cost and Amount Recognized in OCI for All Funded and Unfunded Plans (Details) - Pension Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Interest cost on PBO	$ 46	$ 41	$ 48
Expected return on plan assets	(48)	(53)	(68)
Amortization of losses	13	17	15
Settlement loss	18	17	0
Net pension cost (benefit)	29	22	(5)
Other changes in plan assets and benefit obligations recognized in OCI:
Net (gain) loss	(8)	20	(10)
Amortization of gains	(31)	(33)	(15)
Total recognized in comprehensive income	(39)	(13)	(25)
Total recognized in net pension cost and comprehensive income	$ (10)	$ 9	$ (30)