Employment Benefit Plans (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 11	$ 11	$ 22		$ 21
Interest Cost		21	22	42		44
Expected return on plan assets		(39)	(37)	(79)		(74)
Net cost (credit) recognized		(7)	(4)	(15)		(9)
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		0	1	0		1
Interest Cost		2	2	4		4
Amortization of Prior Service Credit		0	(1)	0		(1)
Net cost (credit) recognized		2	2	4		4
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Defined Benefit Plan Disclosure [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	0	(1)	26	[2]	(1)	[2]
Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Defined Benefit Plan Disclosure [Line Items]
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	[1],[3]	$ 0	$ (1)	$ 0		$ (1)

[1] Reclassifications out of AOCIb Three Months Ended June 30, Details about AOCI Components 2018 2017 Income Statement Line ItemAmortization of pension and retiree health and welfare benefit items Prior service credits — 1 c Total reclassifications for the period $— $1 Net of tax Six Months Ended June 30, Details about AOCI Components 2018 2017 Income Statement Line ItemAmortization of pension and retiree health and welfare benefit items Prior service credits — 1 c Reclassification due to ASU 2018-02 adoption (26) — Total reclassifications for the period $(26) $1 Net of tax

[2] Amounts are net of tax.

[3] Reclassifications out of AOCIb Three Months Ended June 30, Details about AOCI Components 2018 2017 Income Statement Line ItemAmortization of pension and retiree health and welfare benefit items Prior service credits — 1 c Total reclassifications for the period $— $1 Net of tax Six Months Ended June 30, Details about AOCI Components 2018 2017 Income Statement Line ItemAmortization of pension and retiree health and welfare benefit items Prior service credits — 1 c Reclassification due to ASU 2018-02 adoption (26) — Total reclassifications for the period $(26) $1 Net of tax b Amounts in parenthesis indicate debits to the income statement.c This accumulated other comprehensive income component is included in the computation of net periodic pension and retiree health and welfare cost (see Note 9 for additional details).