Benefit Plans - Components of net periodic cost (benefit) (Details) - Pension Plans, Defined Benefit - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plan Disclosure [Line Items]
Interest cost on projected benefit obligation	$ 25	$ 29	$ 77	$ 85
Expected return on plan assets	(38)	(41)	(116)	(121)
Amortization of net actuarial loss	9	9	27	28
Settlement loss	6	0	8	0
Net periodic pension cost (benefit)	2	$ (3)	(4)	$ (8)
Company contributions, pension plans			26
Company contributions, remainder of fiscal year	$ 2		$ 2