Employee Benefit Plans (Details) £ in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2017 GBP (£)	Jun. 30, 2016 USD ($)
Domestic Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 7
Service cost	$ 6	$ 7	12		$ 15
Interest cost	29	32	58		63
Expected return on plan assets	(40)	(41)	(80)		(81)
Net amortization	8	13	15		24
Net periodic benefit cost	3	11	5		21
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			4
Service cost	2	2	4		5
Interest cost	8	8	14		16
Expected return on plan assets	(11)	(10)	(21)		(21)
Net amortization	(4)	(4)	(7)		(7)
Net periodic benefit cost	(5)	(4)	(10)		(7)
UK Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			25	£ 20
Service cost	7	6	13		11
Interest cost	15	19	29		38
Expected return on plan assets	(25)	(29)	(49)		(58)
Net amortization	16	11	33		23
Net periodic benefit cost	$ 13	$ 7	$ 26		$ 14