Investments (Credit Quality of Commercial Mortgage Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 78,675	$ 75,795
Loans Receivable Commercial Mortgage Percentage	100.00%	100.00%
Estimated Fair Value Commercial Mortgage	$ 50,861	$ 48,747
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	85.80%	85.20%
Estimated Fair Value Commercial Mortgage	$ 43,759	$ 41,599
Estimated Fair Value Commercial Mortgage Percentage	86.00%	85.30%
65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	11.40%	12.00%
Estimated Fair Value Commercial Mortgage	$ 5,758	$ 5,849
Estimated Fair Value Commercial Mortgage Percentage	11.30%	12.00%
76% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Receivable Commercial Mortgage Percentage	1.40%	1.40%
Estimated Fair Value Commercial Mortgage	$ 698	$ 664
Estimated Fair Value Commercial Mortgage Percentage	1.40%	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	$ 646	$ 635
Estimated Fair Value Commercial Mortgage Percentage	1.30%	1.30%
Commercial Mortgage Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 49,960	$ 48,463
Commercial Mortgage Loans | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	48,502	47,069
Commercial Mortgage Loans | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	1,270	1,212
Commercial Mortgage Loans | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	188	182
Commercial Mortgage Loans | Less than 65%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	42,853	41,288
Commercial Mortgage Loans | Less than 65% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	41,921	40,360
Commercial Mortgage Loans | Less than 65% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	800	827
Commercial Mortgage Loans | Less than 65% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	132	101
Commercial Mortgage Loans | 65% to 75%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	5,709	5,815
Commercial Mortgage Loans | 65% to 75% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	5,682	5,790
Commercial Mortgage Loans | 65% to 75% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	26	0
Commercial Mortgage Loans | 65% to 75% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	1	25
Commercial Mortgage Loans | 76% to 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	720	688
Commercial Mortgage Loans | 76% to 80% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	397	423
Commercial Mortgage Loans | 76% to 80% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	268	209
Commercial Mortgage Loans | 76% to 80% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	55	56
Commercial Mortgage Loans | Greater than 80%
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	678	672
Commercial Mortgage Loans | Greater than 80% | Greater than 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	502	496
Commercial Mortgage Loans | Greater than 80% | 1.00x - 1.20x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	176	176
Commercial Mortgage Loans | Greater than 80% | Less than 1.00x
Accounts, Notes, Loans and Financing Receivable [Line Items]
Mortgage Loans, Gross	$ 0	$ 0