Employee Benefit Plans (Narrative) (Details) - USD ($) shares in Millions, $ in Millions		12 Months Ended
	Jan. 01, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Percentage of non-matching employer's contribution to eligible participants (as a percent)		1.00%
Employer's Common stock held under 401 (k) plan (in shares)		11
Market value of employer's Common stock held under 401 (k) plan		$ 503
Cash dividend received on employer's Common stock held under 401 (k) plan		14
Accumulated other comprehensive income, unrecognized prior service cost (credit)		2
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments		0	$ 0	$ 0
Accumulated other comprehensive income, unrecognized actuarial losses		824
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		1
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		62
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit obligation		2,700	2,500
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Benefit Obligation		2,300	2,200
Defined Benefit Plan, Plans with Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets		1,800	1,500
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Projected Benefit Obligation		2,600	2,500
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Accumulated Benefit Obligation		2,300	2,200
Defined Benefit Plan, Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets, Aggregate Fair Value of Plan Assets		1,700	1,500
Accumulated benefit obligation		2,700	2,600
Contributions and expected future benefit payments		30
Other Postretirement Benefit Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service years	30 years
Defined Benefit Plan, Recognized Net Gain (Loss) Due to Curtailments		$ 38	$ 0	$ 0
Annual index on credits used to fund Health Care Reimbursement accounts		2.00%
Accumulated other comprehensive income, unrecognized prior service cost (credit)		$ (48)
Accumulated other comprehensive income, unrecognized actuarial losses		42
Prior service cost (credit), expected to be recognized in net periodic benefit cost (credit) in next fiscal year		(13)
Actuarial loss, expected to be recognized in net periodic benefit cost in next fiscal year		$ 4
Annual rate of increase in per capita cost of covered health care benefits assumed for transition period (as a percent)		7.05%
Annual rate for per capita cost of covered health care benefits assumed for 2025 and thereafter (as a percent)		4.60%
Year ultimate rate assumed for per capita cost of health care benefits is to be reached		2025
Contributions and expected future benefit payments		$ 13