Equity (Reclassifications out of Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Realized investment gains (losses), net	$ 432	$ 2,194	$ 4,025
Other income (loss)	1,301	443	0
Total Foreign Currency Translation Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	1	13	17
Net Unrealized Investment Gains (Losses)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	(1,629)	(1,493)	(2,325)
Total amortization of defined benefit pension items
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	224	214	193
Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	(1,404)	(1,266)	(2,115)
Amounts reclassified from AOCI
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Realized investment gains (losses), net	(3)	(13)	(8)
Other income (loss)	2	0	(9)
Amortization of defined benefit items:
Prior service cost	3	8	13
Actuarial gain (loss)	(227)	(222)	(206)
Amounts reclassified from AOCI \| Total Foreign Currency Translation Adjustment
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	(1)	(13)	(17)
Amounts reclassified from AOCI \| Net Unrealized Investment Gains (Losses)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	1,629	1,493	2,325
Amounts reclassified from AOCI \| Total amortization of defined benefit pension items
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	(224)	(214)	(193)
Amounts reclassified from AOCI \| Accumulated Other Comprehensive Income (Loss)
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI	1,404	1,266	2,115
Amounts reclassified from AOCI \| Net unrealized investment gains (losses) on available-for-sale securities
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized investment gains (losses, net	1,647	1,042	2,085
Amounts reclassified from AOCI \| Interest Rate \| Cash Flow Hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized investment gains (losses, net	(2)	(5)	(7)
Amounts reclassified from AOCI \| Currency/Interest Rate \| Cash Flow Hedges
Reclassification Adjustment Out Of Accumulated Other Comprehensive Income [Line Items]
Unrealized investment gains (losses, net	$ (16)	$ 456	$ 247

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(4)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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