Retirement Plans (Narrative) (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) plan	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Plan assets, increase (decrease) for assets transferred to (from) plan				$ 1,600,000,000
Former employees				23,000
Monthly benefit payments				$ 1,000
Settlement loss				$ 424,000,000
Change in basis point for assumptions for next year	25.00%
Defined contribution plan, cost recognized	$ 154,000,000	$ 172,000,000	$ 125,000,000
Number of nonqualified pension plans | plan	2
U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	$ (556,000,000)	(546,000,000)
Expected future benefit payment, next twelve months	580,000,000
Defined benefit plan, plan assets, amount	$ 12,018,000,000	$ 10,165,000,000	$ 8,735,000,000
Actuarial assumptions used to determine benefit obligations, Discount rate	2.60%	3.40%	4.30%
Total recognized in other comprehensive income	$ (532,000,000)
Amount recognized in net periodic benefit cost (credit) and other comprehensive (income) loss, before tax	(500,000,000)	$ (172,000,000)	$ (134,000,000)
Accumulated benefit obligation for defined benefit plans	13,000,000,000.0	11,700,000,000
Settlement loss	0	0	424,000,000
Settlements	$ 0	0
Expected long term return on assets for next year	6.60%
Expected discount rate for next year	2.60%
Rate of compensation increase	2.25%
Expected benefit cost estimate for next fiscal year	$ (114,000,000)
Defined benefit expense	32,000,000	93,000,000	632,000,000
Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	(7,000,000)	(8,000,000)
Defined benefit plan, plan assets, amount	$ 190,000,000	$ 183,000,000	$ 161,000,000
Actuarial assumptions used to determine benefit obligations, Discount rate	2.32%	2.70%	3.97%
Total recognized in other comprehensive income	$ 8,000,000
Amount recognized in net periodic benefit cost (credit) and other comprehensive (income) loss, before tax	13,000,000	$ 24,000,000	$ (6,000,000)
Accumulated benefit obligation for defined benefit plans	246,000,000	236,000,000
Settlement loss	1,000,000	2,000,000	0
Settlements	(5,000,000)	(6,000,000)
Defined benefit expense	5,000,000	6,000,000	4,000,000
Supplemental Employee Retirement Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Benefits paid	(31,000,000)	(26,000,000)	$ (29,000,000)
Expected future benefit payment, next twelve months	21,000,000
Other fixed income
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	(1,585,000,000)	(647,000,000)
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, plan assets, amount	$ 210,000,000	$ 336,000,000