Fair value measurements Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018	Dec. 31, 2017
Derivative Financial Instruments, Liabilities [Member] | Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities			$ 2
Transfers into level 3, liability			0
Transfers out of Level 3, Liabilities			0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities			0
Net Realized Gains/Losses, Liabilities			0
Purchases, Liabilities			0
Sales, Liabilities			0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			0
Balance - End of Period, Liabilities			2
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)			0
Guaranteed Minimum Income Benefit [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Reported liabilities	$ 741		529		$ 861	$ 550
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	452		204
Balance - End of Period, Liabilities	338		167
Guaranteed Minimum Income Benefit [Member] | Guarantees [Member] | Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance - Beginning of Period, Liabilities	452	[1]	204	[2]
Transfers into level 3, liability	0		0
Transfers out of Level 3, Liabilities	0		0
Change in Net Unrealized Gains (Losses) included in OCI, Liabilities	0		0
Net Realized Gains/Losses, Liabilities	(114)		(37)
Purchases, Liabilities	0		0
Sales, Liabilities	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0		0
Balance - End of Period, Liabilities	338	[1]	167	[2]
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ (114)		$ (37)

[1] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $741 million at March 31, 2019, and $861 million at December 31, 2018, which includes a fair value derivative adjustment of $338 million and 452 million, respectively

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $529 million at March 31, 2018, and $550 million at December 31, 2017, which includes a fair value derivative adjustment of $167 million and $204 million, respectively.