Employee Benefit Plans (Details) £ in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2016 GBP (£)	Jun. 30, 2015 USD ($)
Domestic Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			$ 6
Service cost	$ 7	$ 8	15		$ 16
Interest cost	32	31	63		61
Expected return on plan assets	(41)	(43)	(81)		(85)
Net amortization	13	15	24		28
Net periodic benefit cost	11	11	21		20
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	5		6
Interest cost	8	9	16		16
Expected return on plan assets	(10)	(11)	(21)		(23)
Net amortization	(4)	(3)	(7)		(6)
Net periodic benefit cost	(4)	(3)	(7)		(7)
UK Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions			31	£ 22
Service cost	6	6	11		12
Interest cost	19	20	38		40
Expected return on plan assets	(29)	(29)	(58)		(58)
Net amortization	11	16	23		32
Net periodic benefit cost	$ 7	$ 13	$ 14		$ 26