Investments (Credit Quality of Commercial Mortgage Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 79,091	$ 75,795
Loans Receivable Commercial Mortgage Percentage	100.00%	100.00%
Estimated Fair Value Commercial Mortgage Percentage	100.00%	100.00%
Less than 65%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	85.30%	85.20%
Estimated Fair Value Commercial Mortgage Percentage	85.70%	85.30%
65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	12.00%	12.00%
Estimated Fair Value Commercial Mortgage Percentage	11.80%	12.00%
76% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	1.30%	1.40%
Estimated Fair Value Commercial Mortgage Percentage	1.20%	1.40%
Greater than 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	1.40%	1.40%
Estimated Fair Value Commercial Mortgage Percentage	1.30%	1.30%
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 49,898	$ 48,463
Fair Value Mortgage Loans Net Not On Recurring Basis	51,984	48,747
Commercial Mortgage Loans | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	47,854	47,069
Commercial Mortgage Loans | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	1,059	1,212
Commercial Mortgage Loans | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	985	182
Commercial Mortgage Loans | Less than 65%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	42,583	41,288
Fair Value Mortgage Loans Net Not On Recurring Basis	44,529	41,599
Commercial Mortgage Loans | Less than 65% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	41,317	40,360
Commercial Mortgage Loans | Less than 65% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	754	827
Commercial Mortgage Loans | Less than 65% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	512	101
Commercial Mortgage Loans | 65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	5,970	5,815
Fair Value Mortgage Loans Net Not On Recurring Basis	6,150	5,849
Commercial Mortgage Loans | 65% to 75% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	5,708	5,790
Commercial Mortgage Loans | 65% to 75% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	54	0
Commercial Mortgage Loans | 65% to 75% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	208	25
Commercial Mortgage Loans | 76% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	650	688
Fair Value Mortgage Loans Net Not On Recurring Basis	634	664
Commercial Mortgage Loans | 76% to 80% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	368	423
Commercial Mortgage Loans | 76% to 80% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	17	209
Commercial Mortgage Loans | 76% to 80% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	265	56
Commercial Mortgage Loans | Greater than 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	695	672
Fair Value Mortgage Loans Net Not On Recurring Basis	671	635
Commercial Mortgage Loans | Greater than 80% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	461	496
Commercial Mortgage Loans | Greater than 80% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	234	176
Commercial Mortgage Loans | Greater than 80% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 0	$ 0