Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (191)	$ (4,602)	$ (4,220)	$ (4,358)
Amounts arising during the period	(12)	575	315	258
Reclassifications from AOCI	20	100	144	173
Net OCI during the period	8	675	4,037	431
Balance at end of period	(183)	(3,927)	(183)	(3,927)
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
Foreign currency translation adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0	(1,777)	(1,158)	(1,425)
Amounts arising during the period	0	643	372	291
Reclassifications from AOCI	0	0	0	0
Net OCI during the period	0	643	1,158	291
Balance at end of period	0	(1,134)	0	(1,134)
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
Unrealized gains (losses) on qualifying derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	0	8	0	(5)
Amounts arising during the period	0	(52)	(39)	(16)
Reclassifications from AOCI	1	48	25	25
Net OCI during the period	1	(4)	1	9
Balance at end of period	1	4	1	4
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
Defined benefit plans Prior service costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(15)	(16)	(16)	(18)
Amounts arising during the period	0	0	0	0
Reclassifications from AOCI	9	0	2	2
Net OCI during the period	9	0	10	2
Balance at end of period	(6)	(16)	(6)	(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
Defined benefit plans Actuarial gain (loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(176)	(2,817)	(3,046)	(2,910)
Amounts arising during the period	(12)	(16)	(18)	(17)
Reclassifications from AOCI	10	52	117	146
Net OCI during the period	(2)	36	2,868	129
Balance at end of period	$ (178)	$ (2,781)	(178)	$ (2,781)
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