Shareholders' equity AOCI (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance – beginning of period, net of tax	$ 64,021
Other comprehensive income (loss), before income tax	1,047	$ (614)
Other Comprehensive Income (Loss), Tax	43	(9)
Other Comprehensive Income (Loss), Net of Tax	1,004	(605)
Balance – end of period, net of tax	65,726
Total shareholders' equity	70,755	64,431	$ 68,394
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	(3,704)	(4,825)	(4,552)	$ (4,177)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Including Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	843	(796)
Net Realized Gains (Losses) Reclassified from AOCI	(58)	(119)
Other comprehensive income (loss), before income tax	901	(677)
Other Comprehensive Income (Loss), Tax	61	(42)
Other Comprehensive Income (Loss), Net of Tax	840	(635)
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-Sale, Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	(8)	13
AOCI, Liability for Future Policy Benefit, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	(645)	11	(539)	51
AOCI, Liability for Future Policy Benefit, Including Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before income tax	(122)	(53)
Other Comprehensive Income (Loss), Tax	(12)	20
Other Comprehensive Income (Loss), Net of Tax	(110)	(73)
AOCI, Liability for Future Policy Benefit, Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	(4)	(33)
AOCI, Market Risk Benefit, Instrument-Specific Credit Risk, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	(13)	(17)	(16)	(22)
AOCI, Market Risk Benefit, Instrument-Specific Credit Risk, Including Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before income tax	4	5
Other Comprehensive Income (Loss), Tax	1	0
Other Comprehensive Income (Loss), Net of Tax	3	5
AOCI, Market Risk Benefit, Instrument-Specific Credit Risk, Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	0	0
Cumulative Foreign Currency Translation Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	(3,685)	(2,864)	(4,025)	(2,945)
Accumulated Foreign Currency Adjustment Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	367	83
Net Realized Gains (Losses) Reclassified from AOCI	8	3
Other comprehensive income (loss), before income tax	359	80
Other Comprehensive Income (Loss), Tax	12	7
Other Comprehensive Income (Loss), Net of Tax	347	73
Accumulated Foreign Currency Adjustment Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	7	(8)
Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	(22)	13	50	(13)
Accumulated Gain (Loss), Cash Flow Hedge, Including Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), before Reclassifications, before Tax	(26)	(8)
Net Realized Gains (Losses) Reclassified from AOCI	65	(41)
Other comprehensive income (loss), before income tax	(91)	33
Other Comprehensive Income (Loss), Tax	(19)	7
Other Comprehensive Income (Loss), Net of Tax	(72)	26
Accumulated Gain (Loss), Net, Cash Flow Hedge, Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	0	0
Postretirement Benefit Liability Adjustment [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Total shareholders' equity	434	296	438	297
Accumulated Defined Benefit Plans Adjustment Including Portion Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other comprehensive income (loss), before income tax	(4)	(2)
Other Comprehensive Income (Loss), Tax	0	(1)
Other Comprehensive Income (Loss), Net of Tax	(4)	(1)
Accumulated Defined Benefit Plans Adjustment Attributable to Noncontrolling Interest
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	0	0
Accumulated Other Comprehensive Income (Loss) [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Other Comprehensive Income (Loss), Net of Tax	1,009	(577)
Total shareholders' equity	$ (7,635)	$ (7,386)	$ (8,644)	$ (6,809)