Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	$ 34,573	$ 33,047	$ 32,169
Other comprehensive income (loss)	(206)	(198)	42
Ending Balance	34,868	34,573	33,047
Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			(10)
Gains and (Losses) on Cash Flow Hedges
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(2)	(2)	(14)
OCI before reclassifications	(3)	0	11
Amounts reclassified from AOCI	0	0	1
Other comprehensive income (loss)	(3)	0	12
Ending Balance	(5)	(2)	(2)
Gains and (Losses) on Cash Flow Hedges | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			0
Unrealized Gains and (Losses) on Marketable Securities
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	0	10
OCI before reclassifications	0	0	0
Amounts reclassified from AOCI	0	0	0
Other comprehensive income (loss)	0	0	0
Ending Balance	0	0	0
Unrealized Gains and (Losses) on Marketable Securities | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			(10)
Pension and Non-Pension Postretirement Benefit Plan Items (a)
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(3,165)	(2,960)	(2,998)
OCI before reclassifications	(357)	(289)	(143)
Amounts reclassified from AOCI	150	84	181
Other comprehensive income (loss)	(207)	(205)	38
Ending Balance	(3,372)	(3,165)	(2,960)
Pension and Non-Pension Postretirement Benefit Plan Items (a) | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			0
Foreign Currency Items
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(27)	(33)	(23)
OCI before reclassifications	4	6	(10)
Amounts reclassified from AOCI	0	0	0
Other comprehensive income (loss)	4	6	(10)
Ending Balance	(23)	(27)	(33)
Foreign Currency Items | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			0
AOCI of Investments Unconsolidated Affiliates (b)
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	0	0	(1)
OCI before reclassifications	0	(2)	1
Amounts reclassified from AOCI	0	2	0
Other comprehensive income (loss)	0	0	1
Ending Balance	0	0	0
AOCI of Investments Unconsolidated Affiliates (b) | Accounting Standards Update 2016-01 [Member]
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Impact of adoption of Recognition and Measurement of Financial Assets and Liabilities standard			0
Total
Movement in Accumulated Other Comprehensive Income [Roll Forward]
Beginning Balance	(3,194)	(2,995)	(3,026)
OCI before reclassifications	(356)	(285)	(141)
Amounts reclassified from AOCI	150	86	182
Other comprehensive income (loss)	(206)	(199)	41
Ending Balance	$ (3,400)	$ (3,194)	$ (2,995)