Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Federal
Current			$ 28	$ 18	$ 1
Deferred			329	305	403
State
Current			40	26	62
Deferred			21	(14)	(8)
Foreign
Current			16	3	9
Deferred			4	0	(4)
Total income tax expense			438	338	463
Income tax expense allocation
Attributable to income			438	338	463
Stockholders' equity:
Compensation expense for tax purposes in excess of amounts recognized for financial reporting purposes			(5)	(5)	(14)
Tax effect of the change in accumulated other comprehensive loss			$ 59	$ (744)	$ 554
Reconciliation of the statutory federal income tax rate to effective income tax rate
Statutory federal income tax rate (as a percent)			35.00%	35.00%	35.00%
State income taxes, net of federal income tax benefit (as a percent)			2.60%	2.70%	2.80%
Impairment of goodwill (as a percent)			0.00%	0.00%	188.50%
Change in liability for unrecognized tax position (as a percent)			0.40%	0.40%	(24.50%)
Foreign income taxes (as a percent)			0.70%	0.40%	2.70%
Nondeductible accounting adjustment for life insurance (as a percent)			0.00%	0.00%	3.10%
Affiliate debt rationalization, (as a percent)			(2.60%)	(0.00%)	(0.00%)
Release state valuation allowance (as a percent)			0.00%	0.00%	(2.30%)
Research and development credits (as a percent)			(2.10%)	(0.00%)	(0.00%)
Loss on worthless investment in foreigh subsidiary (as a percent)			0.00%	(5.40%)	0.00%
Other, net (as a percent)			(0.70%)	(2.60%)	1.40%
Effective income tax rate (as a percent)			33.30%	30.50%	206.70%
Affiliate debt rationalization	$ 34		$ 34
Research and development credits	28		28
Changes affecting state income taxes	(16)		16	$ 13
Loss on worthless investment in foreign subsidiary		$ (60)
Impairment of goodwill					$ 1,092
Tax settlement with domestic tax authority					(33)
Reversal of liability for unrecognized tax position					22
Nondeductible accounting adjustment for life insurance					17
Release state valuation allowance					5
Deferred tax assets
Post-retirement and pension benefit costs	2,154	2,276	2,154	2,276
Net operating loss carryforwards	487	1,091	487	1,091
Other employee benefits	182	214	182	214
Other	458	602	458	602
Gross deferred tax assets	3,281	4,183	3,281	4,183
Less valuation allowance	(380)	(409)	(380)	(409)
Net deferred tax assets	2,901	3,774	2,901	3,774
Deferred tax liabilities
Property, plant and equipment, primarily due to depreciation differences	(3,841)	(3,869)	(3,841)	(3,869)
Goodwill and other intangible assets	(2,588)	(2,908)	(2,588)	(2,908)
Other	(38)	(147)	(38)	(147)
Gross deferred tax liabilities	(6,467)	(6,924)	(6,467)	(6,924)
Net deferred tax liabilities	(3,566)	(3,150)	(3,566)	(3,150)
Long-term deferred tax liability, net	3,569	3,154	3,569	3,154
Noncurrent deferred tax asset, net	3	4	3	4
Summary of reconciliation of the change in gross unrecognized tax benefits activity
Unrecognized tax benefits, beginning of year			17	14
Increase in tax positions taken in current year			1	0
Increase in tax positions taken in the prior year			7	9
Decrease due to the reversal of tax positions taken in a prior year			(9)	(2)
Decrease from the lapse of statute of limitations			(1)	(1)
Settlements			0	(3)
Unrecognized tax benefits, end of year	15	17	15	17	$ 14
Unrecognized tax benefits that would impact effective tax rate	32	32	32	32
Interest on income taxes accrued	33	$ 30	33	$ 30
Significant change in unrecorded benefit	11		11
Federal
NOLs
Operating loss carryforward	72		72
State
NOLs
Operating loss carryforward	$ 13,000		$ 13,000