Employee Benefit Plans Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Estimated contributions next fiscal year	$ 5
Postemployment Benefits
Postemployment benefit expense	4		$ 3		$ 4
Benefit expense related to deferred compensation plans	1		1		1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	26		25		$ 25
Expected Future Benefit Payments, Fiscal Year Maturity
Benefit Payments - 2018	6
Benefit Payments - 2019	6
Benefit Payments - 2020	7
Benefit Payments - 2021	8
Benefit Payments - 2022	8
Benefit Payments - 2023-2027	42
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	26	[1]	25	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	26		25
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	26	[1]	25	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 2 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	0	[1]	0	[2]
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	0		0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value, Inputs, Level 3 [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Fair value of plan assets	$ 0	[1]	$ 0	[2]
Fixed Income Funds [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit actual plan asset allocations	71.00%		73.00%
U.S. Equity [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit actual plan asset allocations	21.00%		20.00%
International Equity [Member] | Equity Funds [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit actual plan asset allocations	8.00%		7.00%
Benefit Obligation [Member]
Postemployment Benefits
Postemployment benefits liability	$ 14		$ 14
Deferred compensation liability	$ 3		$ 3
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	.15
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | International Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	.02
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	0.68
Minimum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	0
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | U.S. Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	.25
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | International Equity [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	.12
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed Income [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	0.78
Maximum [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and Cash Equivalents [Member]
Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Line Items]
Postretirement benefit plan asset target allocation	0.02

[1] 71% of the amount invested in mutual funds was in fixed income securities; 21% was in U.S. equities and 8% was in international equities.

[2] 73% of the amount invested in mutual funds was in fixed income securities; 20% was in U.S. equities and 7% was in international equities.