Investments (Credit Quality Indicators) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 57,626	$ 55,808
Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,510	3,316
Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	61,136	59,124
0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	31,075	31,024
0%-59.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,405	3,252
0%-59.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	34,480	34,276
60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	18,205	17,159
60%-69.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	105	64
60%-69.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	18,310	17,223
70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	8,054	7,119
70%-79.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
70%-79.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	8,054	7,119
80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	292	506
80% or greater | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
80% or greater | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	292	506
≥ 1.2X | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	55,218	53,519
≥ 1.2X | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,339	3,061
≥ 1.2X | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	58,557	56,580
≥ 1.2X | 0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	30,196	30,325
≥ 1.2X | 0%-59.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	3,234	2,997
≥ 1.2X | 0%-59.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	33,430	33,322
≥ 1.2X | 60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	17,649	16,538
≥ 1.2X | 60%-69.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	105	64
≥ 1.2X | 60%-69.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	17,754	16,602
≥ 1.2X | 70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	7,283	6,324
≥ 1.2X | 70%-79.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
≥ 1.2X | 70%-79.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	7,283	6,324
≥ 1.2X | 80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	90	332
≥ 1.2X | 80% or greater | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
≥ 1.2X | 80% or greater | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	90	332
1.0X to 1.2X | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	2,259	2,055
1.0X to 1.2X | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	157	198
1.0X to 1.2X | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	2,416	2,253
1.0X to 1.2X | 0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	798	538
1.0X to 1.2X | 0%-59.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	157	198
1.0X to 1.2X | 0%-59.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	955	736
1.0X to 1.2X | 60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	556	621
1.0X to 1.2X | 60%-69.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
1.0X to 1.2X | 60%-69.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	556	621
1.0X to 1.2X | 70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	762	754
1.0X to 1.2X | 70%-79.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
1.0X to 1.2X | 70%-79.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	762	754
1.0X to 1.2X | 80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	143	142
1.0X to 1.2X | 80% or greater | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
1.0X to 1.2X | 80% or greater | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	143	142
Less than 1.0X | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	149	234
Less than 1.0X | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	14	57
Less than 1.0X | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	163	291
Less than 1.0X | 0%-59.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	81	161
Less than 1.0X | 0%-59.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	14	57
Less than 1.0X | 0%-59.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	95	218
Less than 1.0X | 60%-69.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 60%-69.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 60%-69.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 70%-79.99% | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	9	41
Less than 1.0X | 70%-79.99% | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 70%-79.99% | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	9	41
Less than 1.0X | 80% or greater | Commercial mortgage loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	59	32
Less than 1.0X | 80% or greater | Agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	0	0
Less than 1.0X | 80% or greater | Commercial mortgage and agricultural property loans
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 59	$ 32