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Fair Value Measurements - Changes in balances of Level 3 financial assets carried at fair value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	$ 1,762	$ 1,636	$ 1,355
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(39)	(35)	(31)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	17	21	(28)
Purchases and issuances	1,079	347	543
Sales and settlements	(437)	(217)	(183)
Transfer into Level 3	289	139	186
Transfer out of Level 3	(381)	(129)	(160)
Sale of subsidiaries			(46)
Financial assets, Ending Balance	2,290	1,762	1,636
Fixed maturities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	1,559	1,470	1,231
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(7)	(14)	(16)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	7	(14)	(19)
Purchases and issuances	1,032	291	460
Sales and settlements	(421)	(189)	(183)
Transfer into Level 3	289	124	186
Transfer out of Level 3	(357)	(109)	(143)
Sale of subsidiaries			(46)
Financial assets, Ending Balance	2,102	1,559	1,470
U.S. government agency
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	8	15	15
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	0	(8)	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	1	0
Purchases and issuances	0	0	0
Sales and settlements	0	0	0
Transfer into Level 3	0	0	0
Transfer out of Level 3	0	0	0
Sale of subsidiaries			0
Financial assets, Ending Balance	8	8	15
State and municipal
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	140	89	100
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	0	0	0
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	2	(4)	(1)
Purchases and issuances	0	57	34
Sales and settlements	(2)	(2)	(1)
Transfer into Level 3	10	0	2
Transfer out of Level 3	(2)	0	(39)
Sale of subsidiaries			(6)
Financial assets, Ending Balance	148	140	89
Residential MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	190	224	300
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(4)	(4)	(11)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	2	(2)	(1)
Purchases and issuances	1	8	0
Sales and settlements	(40)	(28)	(34)
Transfer into Level 3	44	34	86
Transfer out of Level 3	(71)	(42)	(88)
Sale of subsidiaries			(28)
Financial assets, Ending Balance	122	190	224
Commercial MBS
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	25	39	44
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	2	(1)	(1)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	(1)
Purchases and issuances	15	0	0
Sales and settlements	(10)	(7)	(2)
Transfer into Level 3	4	0	4
Transfer out of Level 3	0	(6)	(1)
Sale of subsidiaries			(4)
Financial assets, Ending Balance	36	25	39
Asset-backed securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	484	470	226
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	0	(1)	1
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	1	1	(7)
Purchases and issuances	410	50	265
Sales and settlements	(132)	(52)	(56)
Transfer into Level 3	202	60	53
Transfer out of Level 3	(221)	(44)	(10)
Sale of subsidiaries			(2)
Financial assets, Ending Balance	744	484	470
Corporate and other
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	712	633	546
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(5)	0	(5)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	2	(10)	(9)
Purchases and issuances	606	176	161
Sales and settlements	(237)	(100)	(90)
Transfer into Level 3	29	30	41
Transfer out of Level 3	(63)	(17)	(5)
Sale of subsidiaries			(6)
Financial assets, Ending Balance	1,044	712	633
Equity securities
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	174	140	93
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(21)	(12)	(4)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	10	35	(9)
Purchases and issuances	38	44	77
Sales and settlements	(16)	(28)	0
Transfer into Level 3	0	15	0
Transfer out of Level 3	(20)	(20)	(17)
Sale of subsidiaries			0
Financial assets, Ending Balance	165	174	140
Assets of MIE
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Financial assets, Beginning Balance	29	26	31
Impact of accounting change			0
Total realized/unrealized gains (losses) included in Net earnings	(11)	(9)	(11)
Total realized/unrealized gains (losses) included in other comprehensive income (loss)	0	0	0
Purchases and issuances	9	12	6
Sales and settlements	0	0	0
Transfer into Level 3	0	0	0
Transfer out of Level 3	(4)	0	0
Sale of subsidiaries			0
Financial assets, Ending Balance	$ 23	$ 29	$ 26

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Amount of the impact of accounting change of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount related to the sale of subsidiary of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of gain (loss) recognized in the income statement for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of gain (loss) recognized in other comprehensive income (loss) for financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of purchases of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

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Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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