Shareholders' Equity - Components of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	$ 19,641	$ 17,937
Other comprehensive income (loss) before reclassifications, after tax	(264)	190
Reclassification of losses from accumulated other comprehensive loss, after tax	13	10
Other comprehensive income (loss)	(251)	200
Amounts attributable to noncontrolling interests	20	(17)
Other		(1)
Balance at end of period	19,591	18,034
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	(12)	(5)
Reclassification of losses from accumulated other comprehensive loss, after tax	5	2
Other comprehensive income (loss)	(7)	(3)
Amounts attributable to noncontrolling interests	1	1
Other
Other comprehensive income (loss) before reclassifications, tax	3	1
Reclassification of losses from accumulated other comprehensive loss, tax	(1)	0
Net Unrealized Gains (Losses) on Other Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	(431)	276
Reclassification of losses from accumulated other comprehensive loss, after tax	6	6
Other comprehensive income (loss)	(425)	282
Amounts attributable to noncontrolling interests	34	(24)
Other		(1)
Other comprehensive income (loss) before reclassifications, tax	117	(73)
Reclassification of losses from accumulated other comprehensive loss, tax	(2)	(1)
Cumulative impact of changes in discount rates used to measure long duration contracts
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	214	(114)
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	214	(114)
Amounts attributable to noncontrolling interests	(17)	9
Other
Other comprehensive income (loss) before reclassifications, tax	(57)	31
Reclassification of losses from accumulated other comprehensive loss, tax	0	0
Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	1	(3)
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	1	(3)
Amounts attributable to noncontrolling interests
Other
Other comprehensive income (loss) before reclassifications, tax	0	2
Reclassification of losses from accumulated other comprehensive loss, tax	0	0
Pension and Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	(1)	(1)
Reclassification of losses from accumulated other comprehensive loss, after tax	2	2
Other comprehensive income (loss)	1	1
Amounts attributable to noncontrolling interests
Other
Other comprehensive income (loss) before reclassifications, tax	0	0
Reclassification of losses from accumulated other comprehensive loss, tax	0	0
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Other comprehensive income (loss) before reclassifications, after tax	(35)	37
Reclassification of losses from accumulated other comprehensive loss, after tax
Other comprehensive income (loss)	(35)	37
Amounts attributable to noncontrolling interests	2	(3)
Other
Other comprehensive income (loss) before reclassifications, tax	0	0
Reclassification of losses from accumulated other comprehensive loss, tax	0	0
Accumulated Other Comprehensive Income (Loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(1,067)	(1,867)
Other comprehensive income (loss)	(231)	183
Balance at end of period	(1,298)	(1,685)
Net Unrealized Gains (Losses) on Investments with an Allowance for Credit Losses
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(15)	(13)
Balance at end of period	(21)	(15)
Net Unrealized Gains (Losses) on Other Investments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(907)	(1,720)
Balance at end of period	(1,298)	(1,463)
Cumulative impact of changes in discount rates used to measure long duration contracts
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	176	324
Balance at end of period	373	219
Unrealized Gains (Losses) on Cash Flow Hedges
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	2	9
Balance at end of period	3	6
Pension and Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(212)	(224)
Balance at end of period	(211)	(223)
Foreign Currency Translation
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Balance at beginning of period	(111)	(243)
Balance at end of period	$ (144)	$ (209)