Employee Benefit Plans - Narrative (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	$ 6
Additional estimated contributions by employer during fiscal year	22
Total estimated contributions by employer during fiscal year	28
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	1
Additional estimated contributions by employer during fiscal year	1
Total estimated contributions by employer during fiscal year	2
Postemployment
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Plan assets contributions by employer	14
Additional estimated contributions by employer during fiscal year	16
Total estimated contributions by employer during fiscal year	$ 30