Schedule II - Condensed Financial Information, Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Cash Flows from Operating Activities
Shareholders' net income		$ 813	$ 510	$ 1,411	$ 1,029
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Other liabilities				(159)	(58)
Other, net				48	48
Net cash provided by (used in) operating activities	[1]			2,276	1,267
Cash Flows from Investing Activities
Short term investments purchased				(444)	(401)
Net cash provided by (used in) investing activities	[1]			(732)	(572)
Cash Flows from Financing Activities
Net change in short-term debt				(14)	(111)
Repayment of long-term debt				(250)	0
Issuance of common stock				76	14
Repurchase of common stock				(895)	(139)
Net cash provided by (used in) financing activities				(1,143)	(223)
Net increase (decrease) in cash and cash equivalents				426	486
Cash and cash equivalents, January 1				3,185	1,968
Cash and cash equivalents, June 30		$ 3,611	$ 2,454	$ 3,611	$ 2,454

[1] As required in adopting Accounting Standard Update ("ASU") 2016-15, the Company retrospectively reclassified $71 million of cash distributions from partnership earnings from investing to operating activities for the six months ended June 30, 2016. The comparable amount reported in operating activities in 2017 was $74 million. See Note 2 for further discussion.