Pension and Other Postretirement Benefit Plans (Details 3) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension and Other Postretirement Benefits Plans
Number of shares of common stock included in plan assets	0
401 (k) plans
Employer contributions match	$ 37	$ 34	$ 30
Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	428	407	495
Percentage of plan assets	100.00%	100.00%
Fair value measurement of plan assets
Fair value of plan assets at end of year	428	407	495
Expected future benefit payments
2015	44
2016	58
2017	58
2018	52
2019	53
2020-2024	292
Pension Benefits | Qualified Plans
Contributions
Expected contribution in 2014	30
Pension Benefits | Non-Qualified Plans
Contributions
Expected contribution in 2014	9
Other Postretirement Benefits
Expected future benefit payments
2015	1
2016	1
2017	2
2018	2
2019	2
2020-2024	10
Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	428	407
Fair value measurement of plan assets
Fair value of plan assets at end of year	428	407
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	24	27
Fair value measurement of plan assets
Fair value of plan assets at end of year	24	27
Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	336	299
Fair value measurement of plan assets
Fair value of plan assets at end of year	336	299
Significant Unobservable Inputs (Level 3) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	68	81
Fair value measurement of plan assets
Fair value of plan assets at beginning of year	81	75
Unrealized gains		8
Realized gains (losses)	1
Purchases and sales	(14)	(2)
Fair value of plan assets at end of year	68	81
Cash and cash equivalents | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	1.00%	1.00%
Cash and cash equivalents | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	3	6
Fair value measurement of plan assets
Fair value of plan assets at end of year	3	6
Cash and cash equivalents | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	3	6
Fair value measurement of plan assets
Fair value of plan assets at end of year	3	6
U.S. large-cap | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	17.00%	14.00%
U.S. large-cap | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	72	58
Fair value measurement of plan assets
Fair value of plan assets at end of year	72	58
U.S. large-cap | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	72	58
Fair value measurement of plan assets
Fair value of plan assets at end of year	72	58
U.S. mid-cap growth | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	4.00%	4.00%
U.S. mid-cap growth | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	16	15
Fair value measurement of plan assets
Fair value of plan assets at end of year	16	15
U.S. mid-cap growth | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	16	15
Fair value measurement of plan assets
Fair value of plan assets at end of year	16	15
International large-cap value | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	19.00%	17.00%
International large-cap value | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	80	69
Fair value measurement of plan assets
Fair value of plan assets at end of year	80	69
International large-cap value | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	80	69
Fair value measurement of plan assets
Fair value of plan assets at end of year	80	69
Emerging markets growth | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	1.00%	1.00%
Emerging markets growth | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	5	5
Fair value measurement of plan assets
Fair value of plan assets at end of year	5	5
Emerging markets growth | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	5	5
Fair value measurement of plan assets
Fair value of plan assets at end of year	5	5
Domestic real estate | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	6.00%	7.00%
Domestic real estate | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	24	27
Fair value measurement of plan assets
Fair value of plan assets at end of year	24	27
Domestic real estate | Quoted Prices in Active Markets for Identical Assets (Level 1) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	24	27
Fair value measurement of plan assets
Fair value of plan assets at end of year	24	27
Fixed income | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	37.00%	35.00%
Fixed income | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	158	144
Fair value measurement of plan assets
Fair value of plan assets at end of year	158	144
Fixed income | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	158	144
Fair value measurement of plan assets
Fair value of plan assets at end of year	158	144
Partnership and joint venture interests | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	6.00%	8.00%
Partnership and joint venture interests | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	26	31
Fair value measurement of plan assets
Fair value of plan assets at end of year	26	31
Partnership and joint venture interests | Significant Unobservable Inputs (Level 3) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	26	31
Fair value measurement of plan assets
Fair value of plan assets at beginning of year	31	31
Unrealized gains		2
Realized gains (losses)	(1)
Purchases and sales	(4)	(2)
Fair value of plan assets at end of year	26	31
Insurance contracts at contract value | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	2	2
Fair value measurement of plan assets
Fair value of plan assets at end of year	2	2
Insurance contracts at contract value | Significant Observable Inputs (Level 2) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	2	2
Fair value measurement of plan assets
Fair value of plan assets at end of year	2	2
Hedge funds | Pension Benefits
Pension and Other Postretirement Benefits Plans
Percentage of plan assets	9.00%	13.00%
Hedge funds | Total | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	42	50
Fair value measurement of plan assets
Fair value of plan assets at end of year	42	50
Hedge funds | Significant Unobservable Inputs (Level 3) | Pension Benefits
Pension and Other Postretirement Benefits Plans
Fair value of plan assets	42	50
Fair value measurement of plan assets
Fair value of plan assets at beginning of year	50	44
Unrealized gains		6
Realized gains (losses)	2
Purchases and sales	(10)
Fair value of plan assets at end of year	$ 42	$ 50