Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (3,882)	$ (4,366)	$ (4,220)	$ (4,358)
Amounts arising during the period	54	(264)	327	(317)
Reclassifications from AOCI	59	28	124	73
Net OCI during the period	3,691	(236)	4,029	(244)
Balance at end of period	(191)	(4,602)	(191)	(4,602)
Amounts Reclassified From Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) due to Sale of U.K. Utility Business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from AOCI	3,578		3,578
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(855)	(1,486)	(1,158)	(1,425)
Amounts arising during the period	69	(291)	372	(352)
Reclassifications from AOCI	0	0	0	0
Net OCI during the period	855	(291)	1,158	(352)
Balance at end of period	0	(1,777)	0	(1,777)
Foreign currency translation adjustments [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) due to Sale of U.K. Utility Business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from AOCI	786		786
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(5)	0	0	(5)
Amounts arising during the period	(9)	28	(39)	36
Reclassifications from AOCI	(1)	(20)	24	(23)
Net OCI during the period	5	8	0	13
Balance at end of period	0	8	0	8
Unrealized gains (losses) on qualifying derivatives [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) due to Sale of U.K. Utility Business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from AOCI	15		15
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(16)	(17)	(16)	(18)
Amounts arising during the period	0	0	0	0
Reclassifications from AOCI	(7)	1	(7)	2
Net OCI during the period	1	1	1	2
Balance at end of period	(15)	(16)	(15)	(16)
Defined benefit plans Prior service costs [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) due to Sale of U.K. Utility Business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from AOCI	8		8
Defined benefit plans Actuarial gain (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(3,006)	(2,863)	(3,046)	(2,910)
Amounts arising during the period	(6)	(1)	(6)	(1)
Reclassifications from AOCI	67	47	107	94
Net OCI during the period	2,830	46	2,870	93
Balance at end of period	(176)	$ (2,817)	(176)	$ (2,817)
Defined benefit plans Actuarial gain (loss) [Member] | Amounts Reclassified From Accumulated Other Comprehensive Income [Member] | Reclassification out of Accumulated Other Comprehensive Income (Loss) due to Sale of U.K. Utility Business [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications from AOCI	$ 2,769		$ 2,769