Summary of Significant Accounting Policies - Consolidated Statements of Financial Position (Details) - USD ($)	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained income	$ 48,074,000,000		$ 44,033,000,000
Unrealized foreign currency translation adjustments	(59,000,000)		(49,000,000)
Unamortized pension and other postretirement prior service credit	122,000,000		169,000,000
Total AOCI	1,950,000,000		118,000,000
Total shareholders’ equity	25,998,000,000		21,312,000,000		$ 22,551,000,000
Previously reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained income	49,713,000,000		45,708,000,000
Unrealized foreign currency translation adjustments	(68,000,000)		(64,000,000)
Unamortized pension and other postretirement prior service credit	(1,350,000,000)		(1,491,000,000)
Total AOCI	469,000,000		(1,557,000,000)
Total shareholders’ equity	26,156,000,000		21,312,000,000
Impact of change | Impact of change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained income	(1,639,000,000)		(1,675,000,000)
Unrealized foreign currency translation adjustments	9,000,000		15,000,000
Unamortized pension and other postretirement prior service credit	1,472,000,000		1,660,000,000
Total AOCI	1,481,000,000		1,675,000,000
Total shareholders’ equity	$ (158,000,000)	$ (41,000,000)	$ 0	$ 0