Schedule II - Condensed Financial Information, Statements of Cash Flows (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Cash Flows from Operating Activities
Shareholders' net income		$ 560	$ 456	$ 1,971	$ 1,485
Adjustments to reconcile shareholders' net income to net cash provided by (used in) operating activities:
Other liabilities				221	9
Debt extinguishment costs		321	0	321	0
Other, net				33	25
Net cash provided by (used in) operating activities	[1]			3,511	3,179
Cash Flows from Investing Activities
Short term investments purchased				(722)	(1,317)
Other, net				0	(101)
Net cash provided by (used in) investing activities	[1]			(1,100)	(1,694)
Cash Flows from Financing Activities
Net change in short-term debt				(16)	(143)
Net proceeds on issuance of long-term debt				1,584	0
Repayment of long-term debt				(1,250)	0
Issuance of common stock				111	23
Repurchase of common stock				(1,961)	(139)
Net cash provided by (used in) financing activities				(1,968)	(255)
Net increase (decrease) in cash and cash equivalents				471	1,256
Cash and cash equivalents, January 1				3,185	1,968
Cash and cash equivalents, September 30		$ 3,656	$ 3,224	$ 3,656	$ 3,224

[1] As required in adopting Accounting Standard Update ("ASU") 2016-15, the Company retrospectively reclassified $105 million of cash distributions from partnership earnings from investing to operating activities for the nine months ended September 30, 2016. The comparable amount reported in operating activities in 2017 was $114 million. See Note 2 for further discussion.