Investments (Credit Quality of Mortgage Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 15,728	$ 13,652
Mortgage Loans | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment as a % of Total	99.00%	99.00%
Mortgage Loans | Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 9,694	$ 8,502
Recorded Investment as a % of Total	100.00%	100.00%
Estimated Fair Value of Recorded Investment	$ 10,131	$ 8,584
Estimated Fair Value of Recorded Investment as a % of Total	100.00%	100.00%
Mortgage Loans | Commercial | Debt Service Coverage Ratio, Greater than 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 9,230	$ 8,347
Mortgage Loans | Commercial | Debt Service Coverage Ratio, 1.00x to 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	298	89
Mortgage Loans | Commercial | Debt Service Coverage Ratio, Less than 1.00x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	166	66
Mortgage Loans | Commercial | Loan-to-Value Ratio, Less than 65%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 8,730	$ 7,567
Recorded Investment as a % of Total	90.10%	89.00%
Estimated Fair Value of Recorded Investment	$ 9,142	$ 7,642
Estimated Fair Value of Recorded Investment as a % of Total	90.20%	89.00%
Mortgage Loans | Commercial | Loan-to-Value Ratio, Less than 65% | Debt Service Coverage Ratio, Greater than 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 8,300	$ 7,444
Mortgage Loans | Commercial | Loan-to-Value Ratio, Less than 65% | Debt Service Coverage Ratio, 1.00x to 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	272	89
Mortgage Loans | Commercial | Loan-to-Value Ratio, Less than 65% | Debt Service Coverage Ratio, Less than 1.00x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	158	34
Mortgage Loans | Commercial | Loan-to-Value Ratio, 65% to 75%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 780	$ 786
Recorded Investment as a % of Total	8.00%	9.20%
Estimated Fair Value of Recorded Investment	$ 805	$ 797
Estimated Fair Value of Recorded Investment as a % of Total	8.00%	9.30%
Mortgage Loans | Commercial | Loan-to-Value Ratio, 65% to 75% | Debt Service Coverage Ratio, Greater than 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 746	$ 762
Mortgage Loans | Commercial | Loan-to-Value Ratio, 65% to 75% | Debt Service Coverage Ratio, 1.00x to 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	26	0
Mortgage Loans | Commercial | Loan-to-Value Ratio, 65% to 75% | Debt Service Coverage Ratio, Less than 1.00x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	8	24
Mortgage Loans | Commercial | Loan-to-Value Ratio, 76% to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 184	$ 149
Recorded Investment as a % of Total	1.90%	1.80%
Estimated Fair Value of Recorded Investment	$ 184	$ 145
Estimated Fair Value of Recorded Investment as a % of Total	1.80%	1.70%
Mortgage Loans | Commercial | Loan-to-Value Ratio, 76% to 80% | Debt Service Coverage Ratio, Greater than 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 184	$ 141
Mortgage Loans | Commercial | Loan-to-Value Ratio, 76% to 80% | Debt Service Coverage Ratio, 1.00x to 1.20x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	0	0
Mortgage Loans | Commercial | Loan-to-Value Ratio, 76% to 80% | Debt Service Coverage Ratio, Less than 1.00x
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	0	8
Mortgage Loans | Agricultural
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 3,326	$ 2,874
Recorded Investment as a % of Total	100.00%	100.00%
Estimated Fair Value of Recorded Investment	$ 3,400	$ 2,900
Mortgage Loans | Agricultural | Loan-to-Value Ratio, Less than 65%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 3,130	$ 2,551
Recorded Investment as a % of Total	94.10%	88.80%
Mortgage Loans | Agricultural | Loan-to-Value Ratio, 65% to 75%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 196	$ 322
Recorded Investment as a % of Total	5.90%	11.20%
Mortgage Loans | Agricultural | Loan-to-Value Ratio, 76% to 80%
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 0	$ 1
Recorded Investment as a % of Total	0.00%	0.00%
Mortgage Loans | Residential
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 2,708	$ 2,276
Recorded Investment as a % of Total	100.00%	100.00%
Estimated Fair Value of Recorded Investment	$ 2,800	$ 2,300
Mortgage Loans | Residential | Performing
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 2,671	$ 2,240
Recorded Investment as a % of Total	98.60%	98.40%
Mortgage Loans | Residential | Nonperforming
Financing Receivable, Credit Quality Indicator [Line Items]
Recorded Investment	$ 37	$ 36
Recorded Investment as a % of Total	1.40%	1.60%