Fair Value (Reconciliation of Assets Measured at Fair Value on a Recurring Basis Using Level 3 Inputs) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 311	$ 241
Purchases	47	46
Sales	(4)	(21)
Net unrealized gains (losses) in accumulated other comprehensive income	5	(2)
Net realized gains in investment and other income	0	7
Balance at end of period	359	271
Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	42	17
Purchases	3	15
Sales	0	0
Net unrealized gains (losses) in accumulated other comprehensive income	1	0
Net realized gains in investment and other income	0	0
Balance at end of period	46	32
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	269	224
Purchases	44	31
Sales	(4)	(21)
Net unrealized gains (losses) in accumulated other comprehensive income	4	(2)
Net realized gains in investment and other income	0	7
Balance at end of period	$ 313	$ 239