Employee Benefit Plans (Narrative) (Details) (USD $) Share data in Millions, unless otherwise specified	3 Months Ended	12 Months Ended	6 Months Ended		12 Months Ended
	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Pension plan voluntary lump-sum payments		$ 296,000,000
Reduction in pension benefit obligation as a result of voluntary lump-sum payments	336,000,000	336,000,000
Change In Pension Funding Status Resulting From Pension Plan Voluntary Lump Sum Payments	40,000,000	40,000,000
Non-cash charge resulting from expensing unrealized actuarial losses in AOCI that relate to liabilities that will be settled as a result of pension plan voluntary lump-sum payments, pre-tax	98,000,000
Percentage of non-matching employer's contribution to eligible participants (as a percent)	1.00%	1.00%
Employer's Common stock held under 401 (k) plan (in shares)	11	11
Market value of employer's Common stock held under 401 (k) plan	596,000,000	596,000,000
Cash dividend received on employer's Common stock held under 401 (k) plan		12,000,000
Estimated increase in projected benefit obligation	200,000,000	200,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Non-cash charge resulting from expensing unrealized actuarial losses in AOCI that relate to liabilities that will be settled as a result of pension plan voluntary lump-sum payments, pre-tax		95,000,000	68,000,000	0	0
Accumulated other comprehensive income, unrecognized actuarial losses	983,000,000	983,000,000
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		2,000,000
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		68,000,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit obligation	2,900,000,000	2,900,000,000			2,200,000,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation	2,600,000,000	2,600,000,000			2,000,000,000
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	1,700,000,000	1,700,000,000			1,600,000,000
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit Obligation	2,800,000,000	2,800,000,000			2,100,000,000
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation	2,500,000,000	2,500,000,000			1,900,000,000
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets	1,700,000,000	1,700,000,000			1,600,000,000
Accumulated benefit obligation	3,000,000,000	3,000,000,000			2,600,000,000
Contributions and expected future benefit payments		38,000,000
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated other comprehensive income, unrecognized prior service cost (credit)	(85,000,000)	(85,000,000)
Accumulated other comprehensive income, unrecognized actuarial losses	80,000,000	80,000,000
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		(18,000,000)
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		7,000,000
Annual rate of increase in per capita cost of covered health care benefits assumed for transition period (as a percent)		7.25%
Annual rate for per capita cost of covered health care benefits assumed for 2022 and thereafter (as a percent)		5.00%
Year ultimate rate assumed for per capita cost of health care benefits is to be reached	2024	2024
Contributions and expected future benefit payments		$ 12,000,000
Maximum [Member] | Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual index on credits used to fund Health Care Reimbursement accounts	3.00%	3.00%